At a Glance

A water feature on the National Mall is retrofitted with a biofiltration wetland system to replicate the functions once provided by the historic riparian wetlands underlaying the site.

Project Description

Constitution Gardens, occupying a quiet section of the National Mall in Washington, D.C. between the Washington Monument and Lincoln Memorial, was dedicated in 1976 to commemorate the American Revolution Bicentennial. The Gardens’ main focal point, a human-built 6.5-acre lake, was not designed to sustain significant aquatic life. The concrete lining of its banks and bottom led to elevated water temperatures during the summer. This, coupled with limited habitat availability, resulted in reduced populations of fish, amphibians, and other aquatic organisms. High waste inputs from geese and other waterfowl further degraded lake water quality. The lake resides in a low-lying area along the Potomac River floodplain, where riparian wetlands were historically filled with an unpredictable mosaic of materials, leading to poor soil quality and high flood risk.

After a national competition, the Trust for the National Mall selected PWP Landscape Architecture to redesign Constitution Gardens and restore ecological function to the lake. As a key member of the project team, Biohabitats performed a tree inventory before recommending trees to be preserved, removed, or relocated. Biohabitats then designed a biofiltration wetland system to improve water quality by treating nutrient inputs from stormwater runoff, waterfowl, and other lake organisms.

This system provides deeper depths to enhance habitat and is one of the largest of its kind in Washington, D.C., restoring the function once provided by riparian wetlands and ultimately filtering 11,000,000 gallons of annual stormwater runoff. Constitution Gardens remains an integral part of a busy tourist area that is vulnerable to higher intensity flooding events from the Potomac, underscoring the need for the robust, resilient biofiltration system.



Chesapeake/Delaware Bays

Expertise Areas

Climate Change, Urban Ecology, Water


Trust for the National Mall


Washington, District of Columbia, United States

Project Team
  • PWP Landscape Architecture
  • Martin Aquatic
  • JMT