diff --git a/2021/day6/Cargo.lock b/2021/day6/Cargo.lock
new file mode 100644
index 0000000..a16c0bf
--- /dev/null
+++ b/2021/day6/Cargo.lock
@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "day6"
+version = "0.1.0"
diff --git a/2021/day6/Cargo.toml b/2021/day6/Cargo.toml
new file mode 100644
index 0000000..89d04ae
--- /dev/null
+++ b/2021/day6/Cargo.toml
@@ -0,0 +1,8 @@
+[package]
+name = "day6"
+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/day6/input.txt b/2021/day6/input.txt
new file mode 100644
index 0000000..90498da
--- /dev/null
+++ b/2021/day6/input.txt
@@ -0,0 +1 @@
+1,2,5,1,1,4,1,5,5,5,3,4,1,2,2,5,3,5,1,3,4,1,5,2,5,1,4,1,2,2,1,5,1,1,1,2,4,3,4,2,2,4,5,4,1,2,3,5,3,4,1,1,2,2,1,3,3,2,3,2,1,2,2,3,1,1,2,5,1,2,1,1,3,1,1,5,5,4,1,1,5,1,4,3,5,1,3,3,1,1,5,2,1,2,4,4,5,5,4,4,5,4,3,5,5,1,3,5,2,4,1,1,2,2,2,4,1,2,1,5,1,3,1,1,1,2,1,2,2,1,3,3,5,3,4,2,1,5,2,1,4,1,1,5,1,1,5,4,4,1,4,2,3,5,2,5,5,2,2,4,4,1,1,1,4,4,1,3,5,4,2,5,5,4,4,2,2,3,2,1,3,4,1,5,1,4,5,2,4,5,1,3,4,1,4,3,3,1,1,3,2,1,5,5,3,1,1,2,4,5,3,1,1,1,2,5,2,4,5,1,3,2,4,5,5,1,2,3,4,4,1,4,1,1,3,3,5,1,2,5,1,2,5,4,1,1,3,2,1,1,1,3,5,1,3,2,4,3,5,4,1,1,5,3,4,2,3,1,1,4,2,1,2,2,1,1,4,3,1,1,3,5,2,1,3,2,1,1,1,2,1,1,5,1,1,2,5,1,1,4
diff --git a/2021/day6/src/fish.rs b/2021/day6/src/fish.rs
new file mode 100644
index 0000000..3ec208c
--- /dev/null
+++ b/2021/day6/src/fish.rs
@@ -0,0 +1,48 @@
+const DAYS_TO_CREATE_FISH: u32 = 6;
+const NEW_FISH_EXTRA_DAYS: u32 = 2;
+
+pub fn simulate_spawn(input: &str, days_to_simulate: usize) -> usize {
+    let mut fish_school = input
+        .replace(" ", "")
+        .split('\n')
+        .filter(|line| *line != "")
+        .collect::<Vec<&str>>()
+        .first()
+        .unwrap()
+        .split(',')
+        .map(|s| s.parse().unwrap())
+        .collect::<Vec<u32>>();
+
+    (0..days_to_simulate).for_each(|_| {
+        let mut spawned_fish: Vec<u32> = vec![];
+        fish_school.iter_mut().for_each(|fish| {
+            if *fish == 0 {
+                *fish = DAYS_TO_CREATE_FISH;
+                spawned_fish.push(DAYS_TO_CREATE_FISH + NEW_FISH_EXTRA_DAYS);
+            } else {
+                *fish -= 1;
+            }
+        });
+
+        fish_school.append(&mut spawned_fish);
+    });
+
+    fish_school.len()
+}
+
+#[cfg(test)]
+mod tests {
+
+    use crate::fish::*;
+
+    #[test]
+    fn test_input_example() {
+        let example = "3,4,3,1,2";
+
+        let actual_num_fish_after_18_days = simulate_spawn(example, 18);
+        assert_eq!(actual_num_fish_after_18_days, 26);
+
+        let actual_num_fish_after_80_days = simulate_spawn(example, 80);
+        assert_eq!(actual_num_fish_after_80_days, 5934);
+    }
+}
diff --git a/2021/day6/src/main.rs b/2021/day6/src/main.rs
new file mode 100644
index 0000000..2402fa6
--- /dev/null
+++ b/2021/day6/src/main.rs
@@ -0,0 +1,10 @@
+use std::fs;
+
+pub mod fish;
+
+fn main() {
+    let input = fs::read_to_string("input.txt").expect("Something went wrong reading the file");
+
+    let num_fish = fish::simulate_spawn(&input[..], 80);
+    println!("Num fish after 80 days = {}", num_fish);
+}