diff --git a/common/src/terrain/map.rs b/common/src/terrain/map.rs
index 887cd89990..34c3d434b1 100644
--- a/common/src/terrain/map.rs
+++ b/common/src/terrain/map.rs
@@ -299,6 +299,11 @@ pub struct MapConfig<'a> {
     ///
     /// Defaults to true.
     pub is_water: bool,
+    /// When `is_water` is true, controls whether an ice layer should appear on
+    /// that water.
+    ///
+    /// Defaults to true.
+    pub is_ice: bool,
     /// If true, 3D lighting and shading are turned on.  Otherwise, a plain
     /// altitude map is used.
     ///
@@ -403,6 +408,7 @@ impl<'a> MapConfig<'a> {
 
             is_basement: false,
             is_water: true,
+            is_ice: true,
             is_shaded: true,
             is_temperature: false,
             is_humidity: false,
@@ -581,13 +587,16 @@ impl<'a> MapConfig<'a> {
             let g_water = 32.0 * water_color_factor;
             let b_water = 64.0 * water_color_factor;
             if has_river {
-                let water_rgb = Rgb::new(0, ((g_water) * 1.0) as u8, ((b_water) * 1.0) as u8)
-                    .map(|e| e as f64 / 255.0);
-                rgb = water_rgb;
-                k_s = Rgb::new(1.0, 1.0, 1.0);
-                k_d = water_rgb;
-                k_a = water_rgb;
-                alpha = 0.255;
+                // Rudimentary ice check
+                if !rgb.map(|e| e > 0.6).reduce_and() {
+                    let water_rgb = Rgb::new(0, ((g_water) * 1.0) as u8, ((b_water) * 1.0) as u8)
+                        .map(|e| e as f64 / 255.0);
+                    rgb = water_rgb;
+                    k_s = Rgb::new(1.0, 1.0, 1.0);
+                    k_d = water_rgb;
+                    k_a = water_rgb;
+                    alpha = 0.255;
+                }
             }
 
             let downhill_alt = sample_wpos(downhill_wpos);
diff --git a/world/examples/water.rs b/world/examples/water.rs
index c25451bf90..b66ea79cc2 100644
--- a/world/examples/water.rs
+++ b/world/examples/water.rs
@@ -177,6 +177,7 @@ fn main() {
 
             is_basement,
             is_water,
+            is_ice: true,
             is_shaded,
             is_temperature,
             is_humidity,
diff --git a/world/src/block/mod.rs b/world/src/block/mod.rs
index 0e2aff6eba..e9e40d8ab8 100644
--- a/world/src/block/mod.rs
+++ b/world/src/block/mod.rs
@@ -54,7 +54,7 @@ impl<'a> BlockGen<'a> {
         // Main sample
         let sample = column_gen.get((wpos, index, calendar))?;
 
-        Some(ZCache { sample })
+        Some(ZCache { sample, calendar })
     }
 
     pub fn get_with_z_cache(&mut self, wpos: Vec3<i32>, z_cache: Option<&ZCache>) -> Option<Block> {
@@ -74,8 +74,9 @@ impl<'a> BlockGen<'a> {
             //tree_density,
             //forest_kind,
             //close_structures,
-            // marble,
-            // marble_small,
+            marble,
+            marble_mid,
+            marble_small,
             rock,
             // temp,
             // humidity,
@@ -83,6 +84,8 @@ impl<'a> BlockGen<'a> {
             snow_cover,
             cliff_offset,
             cliff_height,
+            // water_vel,
+            ice_depth,
             ..
         } = sample;
 
@@ -204,8 +207,12 @@ impl<'a> BlockGen<'a> {
             }
         })
         .or_else(|| {
+            let over_water = height < water_height;
             // Water
-            if (wposf.z as f32) < water_height {
+            if over_water && (wposf.z as f32 - water_height).abs() < ice_depth {
+                // TODO: Ice block
+                Some(Block::new(BlockKind::WeakRock, Rgb::new(200, 225, 255)))
+            } else if (wposf.z as f32) < water_height {
                 // Ocean
                 Some(water)
             } else {
@@ -217,6 +224,7 @@ impl<'a> BlockGen<'a> {
 
 pub struct ZCache<'a> {
     pub sample: ColumnSample<'a>,
+    pub calendar: Option<&'a Calendar>,
 }
 
 impl<'a> ZCache<'a> {
@@ -232,7 +240,7 @@ impl<'a> ZCache<'a> {
 
         let ground_max = self.sample.alt + warp + rocks + 2.0;
 
-        let max = ground_max.max(self.sample.water_level + 2.0);
+        let max = ground_max.max(self.sample.water_level + 2.0 + self.sample.ice_depth);
 
         (min, max)
     }
diff --git a/world/src/column/mod.rs b/world/src/column/mod.rs
index 357a373a74..5a3a4fd6bb 100644
--- a/world/src/column/mod.rs
+++ b/world/src/column/mod.rs
@@ -91,6 +91,7 @@ impl<'a> Sampler<'a> for ColumnGen<'a> {
                 wpos,
                 |chunk| if chunk.river.near_water() { 1.0 } else { 0.0 },
             )?;
+        let water_vel = sim.get_interpolated(wpos, |chunk| chunk.river.velocity)?;
         let alt = sim.get_interpolated_monotone(wpos, |chunk| chunk.alt)?;
         let surface_veg = sim.get_interpolated_monotone(wpos, |chunk| chunk.surface_veg)?;
         let sim_chunk = sim.get(chunk_pos)?;
@@ -1081,7 +1082,7 @@ impl<'a> Sampler<'a> for ColumnGen<'a> {
 
         // Snow covering
         let thematic_snow = calendar.map_or(false, |c| c.is_event(CalendarEvent::Christmas));
-        let snow_cover = temp
+        let snow_factor = temp
             .sub(if thematic_snow {
                 CONFIG.tropical_temp
             } else {
@@ -1092,17 +1093,17 @@ impl<'a> Sampler<'a> for ColumnGen<'a> {
             .add(((marble - 0.5) / 0.5) * 0.5)
             .add(((marble_mid - 0.5) / 0.5) * 0.25)
             .add(((marble_small - 0.5) / 0.5) * 0.175);
-        let (alt, ground, sub_surface_color) = if snow_cover <= 0.0 && alt > water_level {
+        let (alt, ground, sub_surface_color) = if snow_factor <= 0.0 && alt > water_level {
             // Allow snow cover.
             (
-                alt + 1.0 - snow_cover.max(0.0),
-                Rgb::lerp(snow, ground, snow_cover),
+                alt + 1.0 - snow_factor.max(0.0),
+                Rgb::lerp(snow, ground, snow_factor),
                 Lerp::lerp(sub_surface_color, ground, alt.sub(basement).mul(0.15)),
             )
         } else {
             (alt, ground, sub_surface_color)
         };
-        let snow_cover = snow_cover <= 0.0;
+        let snow_cover = snow_factor <= 0.0;
 
         // Make river banks not have grass
         let ground = water_dist
@@ -1116,6 +1117,16 @@ impl<'a> Sampler<'a> for ColumnGen<'a> {
         let path = sim.get_nearest_path(wpos);
         let cave = sim.get_nearest_cave(wpos);
 
+        let ice_depth = if snow_factor < -0.25
+            && water_vel.magnitude_squared() < (0.1f32 + marble_mid * 0.2).powi(2)
+        {
+            ((1.0 - Lerp::lerp(marble, Lerp::lerp(marble_mid, marble_small, 0.25), 0.5)) * 5.0
+                - 1.5)
+                .max(0.0)
+        } else {
+            0.0
+        };
+
         Some(ColumnSample {
             alt,
             riverless_alt,
@@ -1149,6 +1160,7 @@ impl<'a> Sampler<'a> for ColumnGen<'a> {
             },
             forest_kind: sim_chunk.forest_kind,
             marble,
+            marble_mid,
             marble_small,
             rock,
             temp,
@@ -1162,6 +1174,8 @@ impl<'a> Sampler<'a> for ColumnGen<'a> {
             snow_cover,
             cliff_offset,
             cliff_height,
+            water_vel,
+            ice_depth,
 
             chunk: sim_chunk,
         })
@@ -1181,6 +1195,7 @@ pub struct ColumnSample<'a> {
     pub tree_density: f32,
     pub forest_kind: ForestKind,
     pub marble: f32,
+    pub marble_mid: f32,
     pub marble_small: f32,
     pub rock: f32,
     pub temp: f32,
@@ -1194,6 +1209,8 @@ pub struct ColumnSample<'a> {
     pub snow_cover: bool,
     pub cliff_offset: f32,
     pub cliff_height: f32,
+    pub water_vel: Vec3<f32>,
+    pub ice_depth: f32,
 
     pub chunk: &'a SimChunk,
 }
diff --git a/world/src/sim/map.rs b/world/src/sim/map.rs
index f2c3b8d3a4..c4599f12bd 100644
--- a/world/src/sim/map.rs
+++ b/world/src/sim/map.rs
@@ -81,6 +81,7 @@ pub fn sample_pos(
 
         is_basement,
         is_water,
+        is_ice,
         is_shaded,
         is_temperature,
         is_humidity,
@@ -133,7 +134,7 @@ pub fn sample_pos(
     let humidity = humidity.min(1.0).max(0.0);
     let temperature = temperature.min(1.0).max(-1.0) * 0.5 + 0.5;
     let wpos = pos * TerrainChunkSize::RECT_SIZE.map(|e| e as i32);
-    let column_rgb_alt = samples
+    let column_data = samples
         .and_then(|samples| {
             chunk_idx
                 .and_then(|chunk_idx| samples.get(chunk_idx))
@@ -162,14 +163,14 @@ pub fn sample_pos(
                 .map(|e| e as f64)
             };
 
-            (rgb, alt)
+            (rgb, alt, sample.ice_depth)
         });
 
     let downhill_wpos = downhill.unwrap_or(wpos + TerrainChunkSize::RECT_SIZE.map(|e| e as i32));
     let alt = if is_basement {
         basement
     } else {
-        column_rgb_alt.map_or(alt, |(_, alt)| alt)
+        column_data.map_or(alt, |(_, alt, _)| alt)
     };
 
     let true_water_alt = (alt.max(water_alt) as f64 - focus.z) / gain as f64;
@@ -189,7 +190,7 @@ pub fn sample_pos(
         if is_shaded { 1.0 } else { alt },
         if is_shaded || is_humidity { 1.0 } else { 0.0 },
     );
-    let column_rgb = column_rgb_alt.map(|(rgb, _)| rgb).unwrap_or(default_rgb);
+    let column_rgb = column_data.map(|(rgb, _, _)| rgb).unwrap_or(default_rgb);
     let mut connections = [None; 8];
     let mut has_connections = false;
     // TODO: Support non-river connections.
@@ -213,33 +214,38 @@ pub fn sample_pos(
                 });
             });
     };
-    let rgb = match (river_kind, (is_water, true_alt >= true_sea_level)) {
-        (_, (false, _)) | (None, (_, true)) | (Some(RiverKind::River { .. }), _) => {
-            let (r, g, b) = (
-                (column_rgb.r
-                    * if is_temperature {
-                        temperature as f64
-                    } else {
-                        column_rgb.r
-                    })
-                .sqrt(),
-                column_rgb.g,
-                (column_rgb.b
-                    * if is_humidity {
-                        humidity as f64
-                    } else {
-                        column_rgb.b
-                    })
-                .sqrt(),
-            );
-            Rgb::new((r * 255.0) as u8, (g * 255.0) as u8, (b * 255.0) as u8)
-        },
-        (None | Some(RiverKind::Lake { .. } | RiverKind::Ocean), _) => Rgb::new(
-            0,
-            ((g_water - water_depth * g_water) * 1.0) as u8,
-            ((b_water - water_depth * b_water) * 1.0) as u8,
-        ),
-    };
+    let rgb =
+        if is_water && is_ice && column_data.map_or(false, |(_, _, ice_depth)| ice_depth > 0.0) {
+            Rgb::new(200, 225, 255)
+        } else {
+            match (river_kind, (is_water, true_alt >= true_sea_level)) {
+                (_, (false, _)) | (None, (_, true)) | (Some(RiverKind::River { .. }), _) => {
+                    let (r, g, b) = (
+                        (column_rgb.r
+                            * if is_temperature {
+                                temperature as f64
+                            } else {
+                                column_rgb.r
+                            })
+                        .sqrt(),
+                        column_rgb.g,
+                        (column_rgb.b
+                            * if is_humidity {
+                                humidity as f64
+                            } else {
+                                column_rgb.b
+                            })
+                        .sqrt(),
+                    );
+                    Rgb::new((r * 255.0) as u8, (g * 255.0) as u8, (b * 255.0) as u8)
+                },
+                (None | Some(RiverKind::Lake { .. } | RiverKind::Ocean), _) => Rgb::new(
+                    0,
+                    ((g_water - water_depth * g_water) * 1.0) as u8,
+                    ((b_water - water_depth * b_water) * 1.0) as u8,
+                ),
+            }
+        };
     // TODO: Make principled.
     let rgb = if is_path {
         Rgb::new(0x37, 0x29, 0x23)