diff --git a/CMakeLists.txt b/CMakeLists.txt
index 8c70bee..c5e5c8a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -3,5 +3,5 @@ project(aoc_2021 C)
 
 set(CMAKE_C_STANDARD 99)
 
-add_executable(aoc_2021 src/main.c src/day_1.c src/day.h src/day_2.c src/puzzle_input.c src/puzzle_input.h src/day_3.c src/day_4.c src/day_5.c src/day_6.c src/day_7.c src/day_8.c)
+add_executable(aoc_2021 src/main.c src/day_1.c src/day.h src/day_2.c src/puzzle_input.c src/puzzle_input.h src/day_3.c src/day_4.c src/day_5.c src/day_6.c src/day_7.c src/day_8.c src/day_9.c src/queue.c src/queue.h)
 target_link_libraries(aoc_2021 m)
diff --git a/inputs/day_9.txt b/inputs/day_9.txt
new file mode 100644
index 0000000..19adf1b
--- /dev/null
+++ b/inputs/day_9.txt
@@ -0,0 +1,100 @@
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\ No newline at end of file
diff --git a/src/day.h b/src/day.h
index 4290ac7..88291db 100644
--- a/src/day.h
+++ b/src/day.h
@@ -9,5 +9,6 @@ int day_5();
 int day_6();
 int day_7();
 int day_8();
+int day_9();
 
 #endif //AOC_2021_DAY_H
diff --git a/src/day_9.c b/src/day_9.c
new file mode 100644
index 0000000..b684d32
--- /dev/null
+++ b/src/day_9.c
@@ -0,0 +1,288 @@
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+
+#include "puzzle_input.h"
+#include "day.h"
+#include "queue.h"
+
+#define MAX_WIDTH 100
+#define QUEUE_SIZE 500
+
+typedef struct {
+    int ii;
+    int jj;
+} point_t;
+
+typedef struct {
+    int8_t map_data[MAX_WIDTH*MAX_WIDTH];
+    uint8_t basin[MAX_WIDTH*MAX_WIDTH];
+    uint8_t basin_count;
+    int16_t line_width;
+} map_data_t;
+
+map_data_t map_data_g = {};
+
+parse_ret_t parse_map_line(char * buffer, void * data, uint16_t index) {
+    map_data_t * map_data = (map_data_t *)data;
+    int8_t * map_line = map_data->map_data + index * MAX_WIDTH;
+
+    int16_t line_ndx = 0;
+    while (buffer[line_ndx] != '\0') {
+        map_line[line_ndx] = buffer[line_ndx] - '0';
+        line_ndx++;
+    }
+
+    map_data->line_width = line_ndx;
+
+    return PARSER_OK;
+}
+
+uint8_t get_map_data(const uint8_t * data, int ii, int jj, uint16_t i_len, uint16_t j_len) {
+    if ((ii >= i_len) || (ii < 0) || (jj >= j_len) || (jj < 0)) {
+        return UINT8_MAX;
+    }
+    else {
+        return *(data + jj + ii * MAX_WIDTH);
+    }
+}
+
+void set_map_data(uint8_t * data, int ii, int jj, uint16_t i_len, uint16_t j_len, uint8_t val) {
+    if ((ii >= i_len) || (ii < 0) || (jj >= j_len) || (jj < 0)) {
+        return;
+    }
+    else {
+        *(data + jj + ii * MAX_WIDTH) = val;
+    }
+}
+
+int8_t is_min(uint8_t * data, int ii, int jj, uint16_t i_len, uint16_t j_len) {
+    uint8_t middle = get_map_data(data, ii, jj, i_len, j_len);
+    uint8_t up = get_map_data(data, ii-1, jj, i_len, j_len);
+    uint8_t down = get_map_data(data, ii+1, jj, i_len, j_len);
+    uint8_t left = get_map_data(data, ii, jj-1, i_len, j_len);
+    uint8_t right = get_map_data(data, ii, jj+1, i_len, j_len);
+
+    if ((middle < up) && (middle < down) && (middle < left) && (middle < right)) {
+        return 1;
+    }
+    else {
+        return 0;
+    }
+}
+
+static void print_map(uint8_t * map, uint16_t max_i, uint16_t max_j) {
+    for (int16_t ii = 0; (int16_t)ii < max_i; ii++) {
+        for (int16_t jj = 0; (int16_t) jj < max_j; jj++) {
+            printf("%u", get_map_data(map, ii, jj, max_i, max_j));
+        }
+        printf("\n");
+    }
+}
+
+static void part_1(uint16_t len) {
+    uint16_t risk_sum = 0;
+    uint8_t basin_count = 1;
+    for (int ii = 0; ii < len; ii++) {
+        for (int jj = 0; jj < map_data_g.line_width; jj++) {
+            if (is_min((uint8_t *)map_data_g.map_data, ii, jj, len, map_data_g.line_width)) {
+                risk_sum += get_map_data((uint8_t *) map_data_g.map_data, ii, jj, len, map_data_g.line_width) + 1;
+                set_map_data(map_data_g.basin, ii, jj, len, map_data_g.line_width, basin_count);
+                basin_count++;
+            }
+        }
+    }
+
+    map_data_g.basin_count = basin_count;
+    printf("PART 1: Low point risk sum is: %d\n", risk_sum);
+}
+
+#define WALL 9
+static queue_ret_t queue_point(queue_t *queue, int pos_i, int pos_j, uint16_t max_i, uint16_t max_j) {
+    point_t point = {0};
+
+    if (get_map_data(map_data_g.basin, pos_i, pos_j, max_i, max_j) > 0) {
+        return QUEUE_OK;
+    }
+
+    if (get_map_data((uint8_t *)map_data_g.map_data, pos_i, pos_j, max_i, max_j) == WALL) {
+        return QUEUE_OK;
+    }
+
+    point.ii = pos_i;
+    point.jj = pos_j;
+
+    if (point.ii > max_i || point.jj > max_j) {
+        printf("Invalid point attempted to be pushed onto queue\n");
+        return QUEUE_DATA_INVALID;
+    }
+
+    return push(queue, &point);
+}
+
+point_t q_data_g[QUEUE_SIZE] = {0};
+static int flood_fill( int pos_i, int pos_j, uint16_t max_i, uint16_t max_j, uint8_t basin_count, uint8_t * basin_counts)
+{
+    queue_t queue = {0};
+    point_t point = {0};
+    queue_ret_t res;
+
+    init(&queue, q_data_g, QUEUE_SIZE, sizeof(point_t));
+
+    point.ii = pos_i;
+    point.jj = pos_j;
+
+    res = push(&queue, &point);
+
+    basin_counts[basin_count - 1] = 1;
+
+    if (res != QUEUE_OK) {
+        printf("Unable to insert element: %d", res);
+        return -1;
+    }
+
+    while (queue.queued_elements > 0) {
+        res = pop(&queue, &point);
+
+        if (res != QUEUE_OK) {
+            printf("Unable to pop element: %d", res);
+            return -1;
+        }
+
+        if (point.ii > max_i || point.jj > max_j) {
+            printf("Invalid point popped from queue\n");
+            return -1;
+        }
+
+        uint8_t val = get_map_data(map_data_g.basin, point.ii, point.jj, max_i, max_j);
+        if (val == 0) {
+            set_map_data(map_data_g.basin, point.ii, point.jj, max_i, max_j, basin_count);
+            basin_counts[basin_count - 1]++;
+        }
+
+        res = queue_point(&queue, point.ii + 1, point.jj, max_i, max_j);
+
+        if (res != QUEUE_OK) {
+            printf("Unable to push element: %d\n", res);
+            return -1;
+        }
+
+        res = queue_point(&queue, point.ii, point.jj + 1, max_i, max_j);
+
+        if (res != QUEUE_OK) {
+            printf("Unable to push element: %d\n", res);
+            return -1;
+        }
+
+        res = queue_point(&queue, point.ii -1, point.jj, max_i, max_j);
+
+        if (res != QUEUE_OK) {
+            printf("Unable to push element: %d\n", res);
+            return -1;
+        }
+
+        res = queue_point(&queue, point.ii, point.jj - 1, max_i, max_j);
+
+        if (res != QUEUE_OK) {
+            printf("Unable to push element: %d\n", res);
+            return -1;
+        }
+
+        //printf("%d: (%d, %d)\n", basin_count, point.ii, point.jj);
+        //print_map(map_data_g.basin, max_i, max_j);
+        //printf("\n");
+    }
+
+    return 0;
+}
+
+static int find_basin(uint8_t basin, uint16_t max_i, uint16_t max_j, int16_t *ret_ii, int16_t *ret_jj) {
+    int found = 0;
+    int16_t ii;
+    int16_t jj;
+
+    for (ii = 0; (int16_t)ii < max_i; ii++) {
+        for (jj= 0; (int16_t)jj < max_j; jj++) {
+          if (get_map_data(map_data_g.basin, ii, jj, max_i, max_j) == basin) {
+              found = 1;
+              break;
+          }
+        }
+
+        if (found) {
+            break;
+        }
+    }
+
+    if (found) {
+        *ret_ii = ii;
+        *ret_jj = jj;
+        return 1;
+    }
+    else {
+        return 0;
+    }
+}
+
+
+
+
+static int uin8t_cmp(const void * a, const void * b) {
+    return ( *(uint8_t *)a - *(uint8_t *)b );
+}
+
+#define BASIN_COUNTS 250
+uint8_t basin_counts[BASIN_COUNTS] = {0};
+static void part_2(uint16_t len) {
+    uint16_t max_i = len;
+    uint16_t max_j = map_data_g.line_width;
+    uint32_t basin_size_multiplied;
+    uint8_t basin_count = map_data_g.basin_count;
+    int16_t basin_ii = 0;
+    int16_t basin_jj = 0;
+
+    if (basin_count - 1 >  BASIN_COUNTS) {
+        printf("Too many basin counts! Need: %u\n", basin_count);
+        return;
+    }
+
+    for (uint8_t basin_ndx = 1; basin_ndx < map_data_g.basin_count; basin_ndx++) {
+
+        if (find_basin(basin_ndx, max_i, max_j, &basin_ii, &basin_jj)) {
+            if (flood_fill(basin_ii, basin_jj, max_i, max_j, basin_ndx, basin_counts) < 0) {
+                printf("Unable to process basin: %d\n", basin_ndx);
+                return;
+            }
+        }
+        else {
+            printf("Basin %u, not found!\n", basin_ndx);
+            return;
+        }
+    }
+
+
+    qsort(basin_counts, basin_count-1, sizeof(uint8_t), uin8t_cmp);
+
+    basin_size_multiplied = basin_counts[basin_count-2] * basin_counts[basin_count - 3] * basin_counts[basin_count - 4];
+
+    printf("PART 2: Multiplying the size of the 3 largest basins gives: %d\n", basin_size_multiplied);
+}
+
+int day_9() {
+    parse_ret_t res;
+    uint16_t len;
+
+    res = read_input_single_line("../inputs/day_9.txt", (void *)&map_data_g, MAX_WIDTH, parse_map_line, &len);
+
+    if (res != PARSER_OK) {
+        printf("Failed to parse input: %d\n", res);
+        return -1;
+    }
+
+    part_1(len);
+    part_2(len);
+
+
+    return 0;
+
+}
\ No newline at end of file
diff --git a/src/main.c b/src/main.c
index c49f7ac..17bb462 100644
--- a/src/main.c
+++ b/src/main.c
@@ -40,6 +40,9 @@ int main(int argc, char * argv[]) {
         case 8:
             day_8();
             break;
+        case 9:
+            day_9();
+            break;
         default:
             printf("Invalid day ding dong!\n");
             return -2;
diff --git a/src/queue.c b/src/queue.c
new file mode 100644
index 0000000..6f4eff6
--- /dev/null
+++ b/src/queue.c
@@ -0,0 +1,46 @@
+#include "string.h"
+#include "queue.h"
+
+static size_t next_element(size_t index, size_t max_len) {
+    return (index + 1) % max_len;
+}
+
+queue_ret_t init(queue_t * queue, void * data, size_t max_data_size, size_t element_size) {
+    queue->data = data;
+    queue->max_data_size = max_data_size;
+    queue->element_size = element_size;
+    queue->queued_elements = 0;
+    queue->pop_ndx = 0;
+    queue->push_ndx = 0;
+
+    return QUEUE_OK;
+}
+
+queue_ret_t push(queue_t * queue, void * element) {
+    if (queue->queued_elements >= queue->max_data_size) {
+        return QUEUE_FULL;
+    }
+
+    memcpy(queue->data + (queue->push_ndx*queue->element_size), element, queue->element_size);
+
+    queue->push_ndx = next_element(queue->push_ndx, queue->max_data_size);
+
+    queue->queued_elements++;
+
+    return QUEUE_OK;
+}
+
+queue_ret_t pop(queue_t * queue, void * store_to) {
+    if (queue->queued_elements == 0) {
+        return QUEUE_EMPTY;
+    }
+
+    memcpy(store_to, queue->data + (queue->pop_ndx*queue->element_size), queue->element_size);
+
+    queue->pop_ndx = next_element(queue->pop_ndx, queue->max_data_size);
+
+    queue->queued_elements--;
+
+    return QUEUE_OK;
+
+}
\ No newline at end of file
diff --git a/src/queue.h b/src/queue.h
new file mode 100644
index 0000000..5eaff2b
--- /dev/null
+++ b/src/queue.h
@@ -0,0 +1,28 @@
+#ifndef AOC_2021_QUEUE_H
+#define AOC_2021_QUEUE_H
+
+#include <stdint.h>
+#include <stddef.h>
+
+typedef enum {
+    QUEUE_OK,
+    QUEUE_FULL = -1,
+    QUEUE_EMPTY = -1,
+    QUEUE_DATA_INVALID = -1,
+} queue_ret_t;
+
+typedef struct {
+    void * data;
+    size_t push_ndx;
+    size_t pop_ndx;
+    size_t queued_elements;
+    size_t max_data_size;
+    size_t element_size;
+} queue_t;
+
+queue_ret_t init(queue_t * queue, void * data, size_t max_data_size, size_t element_size);
+queue_ret_t push(queue_t * queue, void * element);
+queue_ret_t pop(queue_t * queue, void * store_to);
+
+
+#endif //AOC_2021_QUEUE_H