diff --git a/shaders/worldmap_shader.gdshader b/shaders/worldmap_shader.gdshader
index 8184cd7..abfadae 100644
--- a/shaders/worldmap_shader.gdshader
+++ b/shaders/worldmap_shader.gdshader
@@ -4,7 +4,10 @@ uniform sampler2D palette : hint_normal;
 // uniform float tile_width = 8.0;
 uniform float tilemap_width = 512.0;  // Require square tilemap for now
 const float index_scale = 255.0 / 16.0;
-
+const vec2 sea_tile_uv = vec2(0.125, 0.375);
+const vec2 sea_tile_uv_end = vec2(0.25, 0.5);
+const vec2 sea_tile_size = sea_tile_uv_end - sea_tile_uv;
+const vec2 sea_tile_size_inv = 1.0/sea_tile_size;
 
 // This shader maps from tileID texels to Tiles, and then applies palette.
 // tiles hardcoded to 16x16 tiles for now
@@ -17,9 +20,21 @@ vec2 get_tile_atlas_uv(float tile_id, vec2 uv) {
 	vec2 tile_uv = vec2(tile_col, tile_row);  // Convert 15.9375 to vec2(0.9375==15/16, (15)/16), this should result in integer coordinates in [0,15] scaled to [0,15/16] for UV
 	vec2 sub_tile_uv = fract(uv * tilemap_width) / 16.0;
 
-	// TODO: add sea HScroll, waterfall VScroll tile UV modulation
-	return tile_uv + sub_tile_uv;
-	// return sub_tile_uv + vec2(0.0, 0.5);
+	vec2 out_uv = tile_uv + sub_tile_uv;
+
+	// Sea HScroll tile UV modulation
+	// Make this branchless later
+	if (all(greaterThanEqual(out_uv, sea_tile_uv)) && all(lessThan(out_uv, sea_tile_uv_end))) {
+		vec2 sea_tile_uv_diff = out_uv - sea_tile_uv;
+		vec2 pos = sea_tile_uv_diff * sea_tile_size_inv;
+		// pos.x = fract(pos.x + fract(TIME*0.4) + cos(pos.y*0.5) + 20.0*sin(uv.y*20.0));
+		pos.x = fract(pos.x + fract(TIME*0.4) + 20.0*sin(uv.y*20.0));
+		pos.y = fract(pos.y + 0.5*sin(sin(TIME*0.5 + 32.0*uv.x)));
+		out_uv = mix(sea_tile_uv, sea_tile_uv_end, pos);
+	}
+	// TODO: waterfall VScroll UV modulation
+
+	return out_uv;
 }
 
 void fragment() {