Biodiversity Net Gain and Aquatic Habitat Creation in Devon & Cornwall

Reviewed September 2026. Biodiversity Net Gain (BNG) is part of the planning system in England. Unless an exemption applies, development must deliver at least a 10% improvement in biodiversity value, measured with the statutory biodiversity metric.

The rules changed during 2026. From 6 August 2026, planning applications for developments of 0.2 hectares or below are exempt from mandatory BNG. Other exemptions also exist, and local planning policy or separate ecological duties may still apply. The position should therefore be checked for the specific proposal rather than assumed from site size alone.

Where ponds and wetlands fit into BNG

Ponds, scrapes, wet grassland, reedbeds, swales and other aquatic habitats can contribute strongly to a well-designed habitat strategy. Their value is not based simply on digging an area of water. The metric considers habitat type, area, condition, strategic significance, difficulty of creation and the time required to reach the target condition.

A feature must also work physically. Water source, seasonal levels, soil, slopes, connectivity, overflow, pollution risk and long-term management all affect whether the proposed habitat is realistic.

The core BNG process

1. Establish the baseline. Record the existing habitats before works begin and calculate their biodiversity value with the statutory metric.
2. Avoid and minimise loss. Habitat creation should not be used to justify avoidable damage to valuable existing habitat.
3. Design the gain. Set out the habitat types, areas, target conditions and management needed to achieve the required uplift.
4. Secure the commitment. Significant on-site gains and off-site gains normally require legal security, monitoring and management for at least 30 years.
5. Deliver and evidence the work. Construction, planting, establishment and aftercare must follow the approved plan and be documented.

Do you need an ecologist?

For most BNG work, an ecologist should establish the baseline, use the statutory metric and define the habitat targets. Government guidance allows a simpler route for some small developments, but the 2026 exemption changes mean the first task is to establish whether mandatory BNG applies at all.

SAS Aquatics does not replace the project ecologist or planning authority. We work alongside ecologists, landscape teams, landowners and developers to turn aquatic habitat proposals into practical designs, costed scopes and deliverable construction work.

Common reasons aquatic habitat proposals fail

• Choosing a pond location before understanding drainage, groundwater or seasonal levels.
• Using an attractive concept plan that cannot be built or maintained safely.
• Ignoring spoil, access, overflow, pollution pathways or future vegetation management.
• Assuming any new pond automatically creates a high number of biodiversity units.
• Leaving the contractor, ecologist and landscape plan disconnected until work starts.

Useful project information

Early discussions are more productive when they include the site plan, red-line boundary, habitat survey or metric if available, proposed levels, drainage information, access constraints, target habitats and the expected management period.

Official guidance

• Defra: Understanding Biodiversity Net Gain
• Defra: statutory biodiversity metric guidance