diff --git a/2021/day05_hydrothermal_venture/Cargo.toml b/2021/day05_hydrothermal_venture/Cargo.toml
new file mode 100644
index 0000000..69f86e1
--- /dev/null
+++ b/2021/day05_hydrothermal_venture/Cargo.toml
@@ -0,0 +1,8 @@
+[package]
+name = "day05_hydrothermal_venture"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
diff --git a/2021/day05_hydrothermal_venture/challenge.txt b/2021/day05_hydrothermal_venture/challenge.txt
new file mode 100644
index 0000000..98f6b06
--- /dev/null
+++ b/2021/day05_hydrothermal_venture/challenge.txt
@@ -0,0 +1,86 @@
+You come across a field of [hydrothermal vents](https://en.wikipedia.org/wiki/Hydrothermal_vent) on the ocean floor! These vents constantly produce large, opaque clouds, so it would be best to avoid them if possible.
+
+They tend to form in *lines*; the submarine helpfully produces a list of nearby lines of vents (your puzzle input) for you to review. For example:
+
+```
+0,9 -> 5,9
+8,0 -> 0,8
+9,4 -> 3,4
+2,2 -> 2,1
+7,0 -> 7,4
+6,4 -> 2,0
+0,9 -> 2,9
+3,4 -> 1,4
+0,0 -> 8,8
+5,5 -> 8,2
+
+```
+
+Each line of vents is given as a line segment in the format `x1,y1 -> x2,y2` where `x1`,`y1` are the coordinates of one end the line segment and `x2`,`y2` are the coordinates of the other end. These line segments include the points at both ends. In other words:
+
+* An entry like `1,1 -> 1,3` covers points `1,1`, `1,2`, and `1,3`.
+* An entry like `9,7 -> 7,7` covers points `9,7`, `8,7`, and `7,7`.
+
+For now, *only consider horizontal and vertical lines*: lines where either `x1 = x2` or `y1 = y2`.
+
+So, the horizontal and vertical lines from the above list would produce the following diagram:
+
+```
+.......1..
+..1....1..
+..1....1..
+.......1..
+.112111211
+..........
+..........
+..........
+..........
+222111....
+
+```
+
+In this diagram, the top left corner is `0,0` and the bottom right corner is `9,9`. Each position is shown as *the number of lines which cover that point* or `.` if no line covers that point. The top-left pair of `1`s, for example, comes from `2,2 -> 2,1`; the very bottom row is formed by the overlapping lines `0,9 -> 5,9` and `0,9 -> 2,9`.
+
+To avoid the most dangerous areas, you need to determine *the number of points where at least two lines overlap*. In the above example, this is anywhere in the diagram with a `2` or larger - a total of `*5*` points.
+
+Consider only horizontal and vertical lines. *At how many points do at least two lines overlap?*
+
+Your puzzle answer was `6007`.
+
+\--- Part Two ---
+----------
+
+Unfortunately, considering only horizontal and vertical lines doesn't give you the full picture; you need to also consider *diagonal lines*.
+
+Because of the limits of the hydrothermal vent mapping system, the lines in your list will only ever be horizontal, vertical, or a diagonal line at exactly 45 degrees. In other words:
+
+* An entry like `1,1 -> 3,3` covers points `1,1`, `2,2`, and `3,3`.
+* An entry like `9,7 -> 7,9` covers points `9,7`, `8,8`, and `7,9`.
+
+Considering all lines from the above example would now produce the following diagram:
+
+```
+1.1....11.
+.111...2..
+..2.1.111.
+...1.2.2..
+.112313211
+...1.2....
+..1...1...
+.1.....1..
+1.......1.
+222111....
+
+```
+
+You still need to determine *the number of points where at least two lines overlap*. In the above example, this is still anywhere in the diagram with a `2` or larger - now a total of `*12*` points.
+
+Consider all of the lines. *At how many points do at least two lines overlap?*
+
+Your puzzle answer was `19349`.
+
+Both parts of this puzzle are complete! They provide two gold stars: \*\*
+
+At this point, you should [return to your Advent calendar](/2021) and try another puzzle.
+
+If you still want to see it, you can [get your puzzle input](5/input).
\ No newline at end of file
diff --git a/2021/day05_hydrothermal_venture/src/lib.rs b/2021/day05_hydrothermal_venture/src/lib.rs
new file mode 100644
index 0000000..9a907c8
--- /dev/null
+++ b/2021/day05_hydrothermal_venture/src/lib.rs
@@ -0,0 +1,132 @@
+use core::fmt::Display;
+use std::{num::ParseIntError, collections::{HashMap, HashSet}};
+
+#[derive(Debug, PartialEq, Eq)]
+pub enum ParseError {
+    ParseIntError(std::num::ParseIntError),
+    LineMalformed(String),
+}
+
+impl From<ParseIntError> for ParseError {
+    fn from(value: ParseIntError) -> Self {
+        Self::ParseIntError(value)
+    }
+}
+
+impl Display for ParseError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::ParseIntError(e) => write!(f, "Unable to parse into integer: {e}"),
+            Self::LineMalformed(v) => write!(f, "Line is malformed: {v}"),
+        }
+    }
+}
+
+struct Line {
+    start: (usize, usize),
+    end: (usize, usize),
+}
+
+impl TryFrom<&str> for Line {
+    type Error = ParseError;
+
+    fn try_from(value: &str) -> Result<Self, Self::Error> {
+        let ends: Vec<_> = value.split_whitespace().collect();
+        if ends.len() != 3 {
+            return Err(Self::Error::LineMalformed(value.to_string()));
+        }
+
+        let start: Vec<_> = ends[0].split(',').collect();
+        let end: Vec<_> = ends[2].split(',').collect();
+
+        if start.len() != 2 || end.len() != 2 {
+            return Err(Self::Error::LineMalformed(value.to_string()));
+        }
+
+        Ok(Self { 
+            start: (start[0].parse()?, start[1].parse()?), 
+            end: (end[0].parse()?, end[1].parse()?), 
+        })
+    }
+}
+
+impl Line {
+    fn get_horizontal_vertical_coordinates(&self) -> Vec<(usize, usize)> {
+        if self.start.0 == self.end.0 {
+            let x = self.start.0;
+            let min = self.start.1.min(self.end.1);
+            let max = self.start.1.max(self.end.1);
+
+            (min..=max).map(|y| (x, y)).collect()
+        } else if self.start.1 == self.end.1 {
+            let y = self.start.1;
+            let min = self.start.0.min(self.end.0);
+            let max = self.start.0.max(self.end.0);
+
+            (min..=max).map(|x| (x, y)).collect()
+        } else {
+            Vec::new()
+        }
+    }
+
+    fn get_diagonal_coordingates(&self) -> Vec<(usize, usize)> {
+        if self.start.0 < self.end.0 && self.start.1 < self.end.1 {
+            (0..=self.end.0-self.start.0).map(|f| (self.start.0+f, self.start.1+f)).collect()
+        } else if self.start.0 < self.end.0 && self.start.1 > self.end.1 {
+            (0..=self.end.0-self.start.0).map(|f| (self.start.0+f, self.start.1-f)).collect()
+        } else if self.start.0 > self.end.0 && self.start.1 > self.end.1 {
+            (0..=self.start.0-self.end.0).map(|f| (self.start.0-f, self.start.1-f)).collect()
+        } else if self.start.0 > self.end.0 && self.start.1 < self.end.1 {
+            (0..=self.start.0-self.end.0).map(|f| (self.start.0-f, self.start.1+f)).collect()
+        } else {
+            Vec::new()
+        }
+    }
+}
+
+pub fn run(input: &str) -> Result<(usize, usize), ParseError> {
+    let lines: Vec<_> = input.lines().map(Line::try_from).collect::<Result<Vec<_>, _>>()?;
+    let mut all_points = HashSet::new();
+    let mut duplicates = HashSet::new();
+    lines.iter().for_each(|line| {
+        line.get_horizontal_vertical_coordinates().iter().for_each(|coord| {
+            if all_points.contains(coord) {
+                duplicates.insert(*coord);
+            }
+            all_points.insert(*coord);
+        });
+    });
+    let first = duplicates.len();
+    lines.iter().for_each(|line| {
+        line.get_diagonal_coordingates().iter().for_each(|coord| {
+            if all_points.contains(coord) {
+                duplicates.insert(*coord);
+            }
+            all_points.insert(*coord);
+        });
+    });
+    let second = duplicates.len();
+    Ok((first, second))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::fs::read_to_string;
+
+    fn read_file(name: &str) -> String {
+        read_to_string(name).expect(&format!("Unable to read file: {name}")[..]).trim().to_string()
+    }
+
+    #[test]
+    fn test_sample() {
+        let sample_input = read_file("tests/sample_input");
+        assert_eq!(run(&sample_input), Ok((5, 12)));
+    }
+
+    #[test]
+    fn test_challenge() {
+        let challenge_input = read_file("tests/challenge_input");
+        assert_eq!(run(&challenge_input), Ok((6007, 19349)));
+    }
+}
diff --git a/2021/day05_hydrothermal_venture/tests/challenge_input b/2021/day05_hydrothermal_venture/tests/challenge_input
new file mode 100644
index 0000000..22e9364
--- /dev/null
+++ b/2021/day05_hydrothermal_venture/tests/challenge_input
@@ -0,0 +1,500 @@
+818,513 -> 818,849
+259,377 -> 259,599
+120,758 -> 977,758
+49,386 -> 170,386
+773,644 -> 773,745
+510,958 -> 797,671
+480,438 -> 14,904
+475,346 -> 648,173
+620,167 -> 477,310
+632,756 -> 275,756
+225,896 -> 432,896
+582,450 -> 93,450
+402,262 -> 254,410
+915,236 -> 709,236
+338,530 -> 338,375
+243,857 -> 370,984
+32,449 -> 32,26
+672,832 -> 203,363
+426,961 -> 426,402
+108,469 -> 550,27
+567,698 -> 495,770
+25,872 -> 861,36
+12,15 -> 960,963
+986,159 -> 986,765
+912,437 -> 714,437
+476,400 -> 476,873
+125,52 -> 951,878
+633,939 -> 633,641
+12,986 -> 987,11
+783,204 -> 467,520
+547,834 -> 413,700
+879,133 -> 879,890
+409,128 -> 365,128
+913,404 -> 913,598
+798,40 -> 841,40
+279,410 -> 279,758
+935,807 -> 959,783
+389,391 -> 389,38
+271,736 -> 271,865
+70,10 -> 814,10
+694,266 -> 694,92
+860,128 -> 860,966
+755,871 -> 608,871
+519,54 -> 519,833
+817,733 -> 156,72
+553,558 -> 726,558
+152,21 -> 830,699
+529,721 -> 608,721
+744,719 -> 744,221
+962,966 -> 10,14
+863,813 -> 863,984
+138,167 -> 801,830
+926,901 -> 926,769
+170,630 -> 623,177
+281,207 -> 510,207
+41,52 -> 945,956
+100,204 -> 100,43
+177,588 -> 469,588
+946,37 -> 201,782
+669,89 -> 669,868
+945,32 -> 46,931
+673,274 -> 412,274
+424,979 -> 169,979
+774,220 -> 774,571
+684,272 -> 229,272
+621,458 -> 621,884
+222,964 -> 222,608
+953,146 -> 145,954
+442,736 -> 442,230
+471,341 -> 471,124
+632,954 -> 968,954
+492,562 -> 911,981
+485,320 -> 485,349
+888,758 -> 888,23
+271,555 -> 732,555
+932,415 -> 792,275
+399,478 -> 399,472
+543,774 -> 543,261
+422,872 -> 422,715
+524,471 -> 445,471
+573,513 -> 573,762
+721,39 -> 482,39
+379,482 -> 379,479
+70,770 -> 336,770
+797,724 -> 797,364
+498,646 -> 498,410
+756,19 -> 756,83
+901,918 -> 11,918
+572,23 -> 362,23
+814,563 -> 750,627
+279,736 -> 249,706
+509,257 -> 509,897
+127,374 -> 399,102
+421,139 -> 607,139
+79,520 -> 166,607
+491,779 -> 284,986
+395,606 -> 395,164
+958,244 -> 442,760
+493,509 -> 673,509
+76,321 -> 482,727
+903,926 -> 103,126
+729,689 -> 63,23
+956,13 -> 198,771
+973,452 -> 193,452
+282,362 -> 896,976
+68,985 -> 985,68
+148,109 -> 310,109
+852,920 -> 371,439
+334,41 -> 864,571
+258,592 -> 72,778
+259,990 -> 259,308
+480,363 -> 480,751
+943,153 -> 801,153
+755,172 -> 123,804
+355,501 -> 437,501
+666,769 -> 340,769
+982,10 -> 23,969
+886,410 -> 886,669
+454,410 -> 454,218
+426,688 -> 227,688
+969,959 -> 207,959
+586,27 -> 591,22
+852,133 -> 166,819
+587,199 -> 781,199
+78,85 -> 78,394
+468,162 -> 727,162
+261,473 -> 573,473
+924,300 -> 924,873
+651,817 -> 651,600
+717,909 -> 717,187
+898,656 -> 454,656
+805,873 -> 507,873
+529,825 -> 529,217
+578,503 -> 783,503
+929,663 -> 920,663
+332,938 -> 332,381
+710,783 -> 272,783
+505,863 -> 240,863
+146,548 -> 146,849
+71,822 -> 820,73
+875,883 -> 451,883
+983,17 -> 30,970
+646,350 -> 646,330
+618,430 -> 881,430
+398,977 -> 643,732
+839,441 -> 406,874
+948,358 -> 178,358
+26,660 -> 26,612
+418,467 -> 418,115
+899,936 -> 899,611
+770,430 -> 770,648
+653,136 -> 95,694
+645,153 -> 818,153
+622,604 -> 77,59
+470,597 -> 592,719
+753,921 -> 743,921
+507,821 -> 507,275
+696,969 -> 433,969
+48,284 -> 552,284
+391,866 -> 187,866
+571,897 -> 107,433
+24,466 -> 24,186
+949,587 -> 582,587
+541,32 -> 541,583
+12,984 -> 986,10
+124,988 -> 124,904
+209,548 -> 209,12
+828,652 -> 34,652
+455,460 -> 905,910
+632,638 -> 343,638
+371,275 -> 145,275
+66,941 -> 945,62
+672,286 -> 672,301
+447,45 -> 82,410
+665,683 -> 487,683
+410,582 -> 670,842
+917,705 -> 917,323
+122,372 -> 403,653
+970,47 -> 40,977
+15,707 -> 732,707
+666,854 -> 666,256
+640,230 -> 188,230
+71,297 -> 71,472
+51,431 -> 339,431
+957,363 -> 82,363
+844,171 -> 274,171
+184,81 -> 184,786
+437,456 -> 138,456
+326,478 -> 814,966
+956,76 -> 226,806
+399,572 -> 399,877
+923,813 -> 923,898
+445,221 -> 947,723
+85,590 -> 415,590
+644,127 -> 644,140
+372,732 -> 372,522
+413,186 -> 244,186
+291,163 -> 197,69
+889,41 -> 208,722
+835,925 -> 835,616
+790,340 -> 426,340
+26,872 -> 805,93
+617,701 -> 828,701
+344,654 -> 530,654
+940,989 -> 41,90
+642,87 -> 206,523
+306,54 -> 306,761
+672,778 -> 672,868
+29,959 -> 974,14
+458,166 -> 86,166
+565,394 -> 352,181
+516,805 -> 457,805
+464,450 -> 756,450
+177,181 -> 661,181
+962,394 -> 630,62
+94,613 -> 12,613
+932,159 -> 818,273
+640,642 -> 976,642
+184,346 -> 184,22
+370,672 -> 458,672
+235,334 -> 770,869
+207,17 -> 811,17
+351,25 -> 896,25
+589,178 -> 921,510
+672,733 -> 937,733
+159,718 -> 787,90
+598,317 -> 598,455
+591,164 -> 591,374
+276,321 -> 515,321
+245,431 -> 245,350
+268,976 -> 939,305
+319,297 -> 823,297
+246,132 -> 229,132
+338,707 -> 338,59
+723,402 -> 723,739
+539,846 -> 94,846
+879,458 -> 783,458
+400,847 -> 770,477
+111,957 -> 858,210
+640,340 -> 878,578
+613,446 -> 115,446
+119,480 -> 119,425
+447,34 -> 986,34
+730,357 -> 532,555
+85,283 -> 26,283
+834,327 -> 263,898
+739,580 -> 640,481
+841,938 -> 841,123
+987,979 -> 23,15
+827,563 -> 632,563
+313,419 -> 466,572
+323,326 -> 455,326
+976,683 -> 976,314
+896,568 -> 338,568
+733,464 -> 819,464
+613,608 -> 493,608
+178,137 -> 178,663
+262,595 -> 262,308
+535,268 -> 851,268
+653,111 -> 653,723
+947,47 -> 23,971
+351,800 -> 351,806
+143,49 -> 850,756
+872,643 -> 872,265
+946,727 -> 427,727
+354,284 -> 938,868
+652,874 -> 652,447
+920,27 -> 387,27
+816,265 -> 816,366
+238,632 -> 336,534
+593,399 -> 593,425
+696,108 -> 138,666
+828,110 -> 240,698
+421,590 -> 847,590
+409,449 -> 622,449
+986,291 -> 45,291
+580,34 -> 663,34
+921,988 -> 35,102
+619,88 -> 249,88
+48,773 -> 503,773
+277,560 -> 377,460
+139,803 -> 123,787
+339,688 -> 907,120
+775,117 -> 775,203
+237,287 -> 507,557
+27,832 -> 429,430
+70,592 -> 672,592
+701,295 -> 69,295
+723,672 -> 714,672
+974,359 -> 292,359
+439,462 -> 439,973
+681,922 -> 357,922
+402,521 -> 25,521
+297,525 -> 297,227
+763,797 -> 763,153
+737,634 -> 869,634
+379,875 -> 810,875
+427,117 -> 705,117
+785,376 -> 265,896
+922,818 -> 141,37
+61,371 -> 61,432
+557,303 -> 411,303
+573,100 -> 295,100
+767,657 -> 231,657
+11,938 -> 875,74
+782,393 -> 782,502
+899,913 -> 519,533
+887,11 -> 244,654
+730,271 -> 426,271
+555,538 -> 379,538
+871,866 -> 871,461
+934,178 -> 934,845
+741,327 -> 325,327
+332,394 -> 518,580
+673,372 -> 809,236
+951,972 -> 77,98
+985,585 -> 985,55
+604,341 -> 269,676
+408,70 -> 455,23
+718,239 -> 718,522
+15,16 -> 984,985
+743,836 -> 852,836
+407,59 -> 246,220
+388,538 -> 388,587
+978,249 -> 810,249
+506,945 -> 506,644
+657,101 -> 657,522
+879,261 -> 935,261
+751,625 -> 926,800
+676,183 -> 573,286
+272,491 -> 765,984
+867,207 -> 570,207
+117,784 -> 750,784
+883,528 -> 883,845
+430,765 -> 581,614
+748,839 -> 748,775
+265,16 -> 188,93
+894,584 -> 525,215
+278,414 -> 19,673
+588,446 -> 588,656
+469,676 -> 469,354
+383,848 -> 669,848
+212,341 -> 367,341
+988,582 -> 988,825
+296,187 -> 785,187
+255,400 -> 255,286
+756,886 -> 524,654
+966,32 -> 966,940
+711,243 -> 81,873
+207,34 -> 359,186
+555,850 -> 45,850
+41,962 -> 947,56
+15,888 -> 15,795
+773,709 -> 579,515
+228,517 -> 228,334
+495,290 -> 965,290
+462,309 -> 462,421
+945,274 -> 945,735
+547,361 -> 547,140
+37,930 -> 836,930
+987,445 -> 45,445
+25,766 -> 757,34
+643,946 -> 318,621
+507,402 -> 507,981
+22,903 -> 488,437
+887,487 -> 957,487
+57,434 -> 21,398
+688,907 -> 917,678
+146,498 -> 146,965
+375,939 -> 888,426
+966,151 -> 684,433
+160,373 -> 722,373
+410,571 -> 410,683
+588,667 -> 588,337
+832,348 -> 376,804
+567,430 -> 453,430
+368,442 -> 97,442
+11,191 -> 584,764
+647,965 -> 647,331
+576,856 -> 976,456
+205,287 -> 205,495
+677,872 -> 677,246
+21,16 -> 973,968
+949,738 -> 126,738
+921,595 -> 921,370
+539,821 -> 660,821
+143,188 -> 143,793
+639,930 -> 639,454
+522,360 -> 917,755
+128,281 -> 647,800
+456,365 -> 456,34
+434,530 -> 431,530
+549,792 -> 549,892
+414,229 -> 41,602
+289,468 -> 592,771
+555,624 -> 727,452
+187,780 -> 187,838
+807,282 -> 807,968
+52,249 -> 52,332
+797,525 -> 462,190
+295,562 -> 654,921
+862,627 -> 252,627
+22,116 -> 866,960
+155,652 -> 155,979
+598,748 -> 51,748
+130,601 -> 231,601
+468,183 -> 468,414
+208,193 -> 927,912
+25,755 -> 770,755
+667,755 -> 916,506
+395,103 -> 395,468
+763,62 -> 763,153
+371,816 -> 371,109
+508,138 -> 37,609
+464,983 -> 707,983
+282,295 -> 282,536
+646,680 -> 646,775
+95,117 -> 95,62
+606,963 -> 203,963
+403,195 -> 97,195
+743,293 -> 743,815
+243,748 -> 431,748
+953,54 -> 22,985
+693,810 -> 656,810
+163,221 -> 728,786
+187,648 -> 187,337
+98,559 -> 98,165
+903,49 -> 46,906
+600,779 -> 432,779
+500,606 -> 500,878
+812,797 -> 31,16
+204,786 -> 517,786
+952,757 -> 952,923
+66,809 -> 66,831
+479,72 -> 17,72
+96,430 -> 96,932
+346,667 -> 796,667
+731,102 -> 162,102
+755,846 -> 755,135
+90,18 -> 404,18
+828,802 -> 134,108
+278,946 -> 278,765
+289,163 -> 869,743
+134,58 -> 887,58
+354,735 -> 904,185
+897,74 -> 897,716
+508,904 -> 508,719
+285,358 -> 795,868
+51,155 -> 51,643
+579,388 -> 431,240
+79,330 -> 869,330
+955,863 -> 140,48
+800,473 -> 689,473
+711,128 -> 918,128
+787,166 -> 787,36
+257,684 -> 873,68
+984,986 -> 10,12
+76,580 -> 660,580
+265,868 -> 955,868
+569,491 -> 466,594
+535,654 -> 37,654
+889,751 -> 411,273
+681,491 -> 600,491
+459,721 -> 459,109
+824,130 -> 689,265
+406,780 -> 406,965
+18,31 -> 904,917
+179,91 -> 232,38
+280,552 -> 428,700
+967,980 -> 19,32
+47,289 -> 738,980
+160,592 -> 120,592
+710,412 -> 28,412
+40,430 -> 747,430
+435,821 -> 747,509
+36,741 -> 36,363
+787,30 -> 847,30
+725,968 -> 725,940
+739,356 -> 27,356
+65,193 -> 419,193
+318,513 -> 404,513
+150,230 -> 150,968
+847,410 -> 847,505
+950,188 -> 950,278
+816,312 -> 587,541
+980,145 -> 154,145
+79,781 -> 616,781
+433,284 -> 433,309
+624,264 -> 569,264
+604,859 -> 570,825
+936,691 -> 350,105
+259,631 -> 648,242
+445,27 -> 445,872
+438,689 -> 977,150
+718,603 -> 718,327
+967,310 -> 98,310
+439,381 -> 439,35
+645,240 -> 282,240
+475,54 -> 475,658
+972,610 -> 759,823
diff --git a/2021/day05_hydrothermal_venture/tests/sample_input b/2021/day05_hydrothermal_venture/tests/sample_input
new file mode 100644
index 0000000..b258f68
--- /dev/null
+++ b/2021/day05_hydrothermal_venture/tests/sample_input
@@ -0,0 +1,10 @@
+0,9 -> 5,9
+8,0 -> 0,8
+9,4 -> 3,4
+2,2 -> 2,1
+7,0 -> 7,4
+6,4 -> 2,0
+0,9 -> 2,9
+3,4 -> 1,4
+0,0 -> 8,8
+5,5 -> 8,2