diff --git a/counterexamples/base/bathymetry/bad-depth.yaml b/counterexamples/base/bathymetry/bad-depth.yaml
new file mode 100644
index 000000000..bc4e25c56
--- /dev/null
+++ b/counterexamples/base/bathymetry/bad-depth.yaml
@@ -0,0 +1,17 @@
+---
+id: "overture:bathymetry:counterexample:bad-depth"
+type: Feature
+geometry:
+  type: Polygon
+  coordinates: [[[-73.1902319,41.6678018],[-73.1896302,41.667817],[-73.1890448,41.6667723],[-73.1899188,41.6666994],[-73.1902319,41.6678018]]]
+properties:
+  theme: base
+  type: bathymetry
+  version: 0
+  depth: 1
+  sources:
+    - record_id: x123
+      property: ""
+      dataset: some source
+  ext_expected_errors:
+    - "depth/maximum]: maximum: got 1, want 0"
diff --git a/counterexamples/base/bathymetry/missing-depth.yaml b/counterexamples/base/bathymetry/missing-depth.yaml
new file mode 100644
index 000000000..01fffe2b5
--- /dev/null
+++ b/counterexamples/base/bathymetry/missing-depth.yaml
@@ -0,0 +1,12 @@
+---
+id: "overture:bathymetry:counterexample:bad-depth"
+type: Feature
+geometry:
+  type: Polygon
+  coordinates: [[[-73.1902319,41.6678018],[-73.1896302,41.667817],[-73.1890448,41.6667723],[-73.1899188,41.6666994],[-73.1902319,41.6678018]]]
+properties:
+  theme: base
+  type: bathymetry
+  version: 0
+  ext_expected_errors:
+    - "missing property 'depth'"
diff --git a/docs/schema/reference/base/bathymetry.mdx b/docs/schema/reference/base/bathymetry.mdx
new file mode 100644
index 000000000..a68e33e0a
--- /dev/null
+++ b/docs/schema/reference/base/bathymetry.mdx
@@ -0,0 +1,55 @@
+---
+title: bathymetry
+---
+
+import CodeBlock from '@theme/CodeBlock';
+import JSONSchemaViewer from "@theme/JSONSchemaViewer";
+import generateResolverOptions from "@site/src/components/shared-libs/generateResolverOptions"
+import yamlLoad from "@site/src/components/yamlLoad"
+import BathymetrySchema from "!!raw-loader!@site/docs/_schema/base/bathymetry.yaml";
+
+import BathymetryExample from "!!raw-loader!@site/docs/_examples/base/bathymetry-example.yaml";
+
+import Tabs from '@theme/Tabs';
+import TabItem from '@theme/TabItem';
+
+# Bathymetry
+
+<table>
+  <tbody>
+  <tr>
+    <th>Geometry Type</th>
+    <td>
+      <code>Polygon</code> or <code>MultiPolygon</code>
+    </td>
+  </tr>
+  <tr>
+    <th>Theme</th>
+    <td><code>base</code></td>
+  </tr>
+  <tr>
+    <th>Type</th>
+    <td><code>bathymetry</code></td>
+  </tr>
+  </tbody>
+</table>
+
+## Schema
+
+<Tabs>
+  <TabItem value="browsable" label="Browsable" default>
+    <JSONSchemaViewer schema={ yamlLoad(BathymetrySchema) } resolverOptions={ generateResolverOptions({remote: true, yamlBasePath: '/base'})}/>
+  </TabItem>
+  <TabItem value="yaml" label="YAML" default>
+    <CodeBlock language="jsx">{BathymetrySchema}</CodeBlock>
+  </TabItem>
+</Tabs>
+
+## Examples
+
+<Tabs>
+  <TabItem value="1" label="bathymetry" default>
+    <CodeBlock language="json">{ JSON.stringify(yamlLoad(BathymetryExample), null, 2) }</CodeBlock>
+  </TabItem>
+
+</Tabs>
diff --git a/examples/base/bathymetry-example.yaml b/examples/base/bathymetry-example.yaml
new file mode 100644
index 000000000..5408c60a2
--- /dev/null
+++ b/examples/base/bathymetry-example.yaml
@@ -0,0 +1,19 @@
+---
+id: "overture:bathymetry:example:1"
+type: Feature
+geometry:
+  type: Polygon
+  coordinates: [[[-73.1902319,41.6678018],[-73.1896302,41.667817],[-73.1890448,41.6667723],[-73.1899188,41.6666994],[-73.1902319,41.6678018]]]
+properties:
+  theme: base
+  type: bathymetry
+  depth: -2500
+  cartography:
+    min_zoom: 0
+    max_zoom: 23
+    sort_key: 7
+  sources:
+    - record_id: x123
+      property: ""
+      dataset: some source
+  version: 0
diff --git a/schema/base/bathymetry.yaml b/schema/base/bathymetry.yaml
new file mode 100644
index 000000000..dd529d7e6
--- /dev/null
+++ b/schema/base/bathymetry.yaml
@@ -0,0 +1,22 @@
+---
+"$schema": https://json-schema.org/draft/2020-12/schema
+title: bathymetry
+description: Topographic representation of an underwater area, such as a part of the ocean floor.
+type: object
+properties:
+  id:
+    "$ref": ../defs.yaml#/$defs/propertyDefinitions/id
+  geometry:
+    unevaluatedProperties: false
+    oneOf:
+      - "$ref": https://geojson.org/schema/Polygon.json
+      - "$ref": https://geojson.org/schema/MultiPolygon.json
+  properties:
+    unevaluatedProperties: false
+    allOf:
+      - "$ref": ../defs.yaml#/$defs/propertyContainers/overtureFeaturePropertiesContainer
+      - "$ref": ../defs.yaml#/$defs/propertyContainers/levelContainer
+      - "$ref": ../defs.yaml#/$defs/propertyContainers/cartographyContainer
+    required: [depth]
+    properties:
+      depth: { "$ref": "./defs.yaml#/$defs/propertyDefinitions/depth" }
diff --git a/schema/base/defs.yaml b/schema/base/defs.yaml
index 3fde45628..3f0cc0cb7 100644
--- a/schema/base/defs.yaml
+++ b/schema/base/defs.yaml
@@ -8,6 +8,10 @@ description: Common schema definitions the base theme (primarily from OSM)
       description: Elevation above sea level (in meters) of the feature.
       type: integer
       maximum: 9000
+    depth:
+      description: Depth below surface level (in meters) of the feature.
+      type: integer
+      maximum: 0
     height:
       description: >-
         Height of the feature in meters.
diff --git a/schema/defs.yaml b/schema/defs.yaml
index 27ec31fa3..d86fbf4e5 100644
--- a/schema/defs.yaml
+++ b/schema/defs.yaml
@@ -21,6 +21,7 @@ description: Common schema definitions shared by all themes
       type: string
       enum:
         - address
+        - bathymetry
         - building
         - connector
         - division
diff --git a/schema/schema.yaml b/schema/schema.yaml
index 25e8dd6b5..df59e6529 100644
--- a/schema/schema.yaml
+++ b/schema/schema.yaml
@@ -18,6 +18,14 @@ oneOf:
             type: { enum: [address] }
     then: { "$ref": addresses/address.yaml }
     else: { propertyNames: false }
+  - if:
+      properties:
+        properties:
+          properties:
+            theme: { enum: [base] }
+            type: { enum: [bathymetry] }
+    then: { "$ref": base/bathymetry.yaml }
+    else: { propertyNames: false }
   - if:
       properties:
         properties: