National Zoo    - Part of the Smithsonian Institution. General information, animal webcams, videos, and photos, educational games, online animal demonstrations, a virtual zoo tour, and online presentations by the director and other staff.

Friends of the National Zoo (FONZ) - Membership group providing support to the National Zoo.

National Aquarium - News and information, hours, directions, events, and a page of games and activities for children.

ZooGoer Magazine - A conservation and wildlife magazine published for the Friends of the National Zoo.

Dumbarton Oaks - Gardens at the Washington (D.C.) academic library, designed by Beatrix Farrand, which complement its research resources in the history of landscape architecture. Garden tour in photos.

The National Garden - Series of display gardens next to the U.S. Botanic Garden on the Capitol Grounds. Completely Flash-driven website with information and graphics.

United States National Arboretum - Contains an array of display gardens, collections, and historical monuments set among native stands of eastern deciduous trees. Photo galleries, information about events and research, and horticultural information.

Virtual Tour of The Gardens at Dumbarton Oaks - A presentation of 50 photos of the Gardens, along with brief annotations.

Friends of the National Arboretum - FONA - An independent, non-profit organization established to enhance support for the U.S. National Arboretum. Includes information on its activities, such as the annual garden fair and the Youth Garden for city children, calendar of events, newsletter, and membership form.

Kenilworth Park and Aquatic Gardens - Aquatic plants are propagated and displayed in this park on the Anacostia River, operated by the National Park Service, alongside a tidal marsh and recreational areas.

The National Garden - Offers a major American public garden comprising a center for environmental, horticultural and botanical education. Includes plans, events and sponsorship opportunities.

The United States Botanic Garden - Features a variety of living exhibits, including seasonal exhibits in the conservatory and Bartholdi Park. Features FAQ, events, plant collections and a virtual tour.

United States National Arboretum - Contains an array of display gardens, collections, and historical monuments set among native stands of eastern deciduous trees.

Anacostia Park - Includes Kenilworth March, Kenilworth Park and Aquatic Gardens, the Langston Golf Course, ballfields, ball courts, picnic areas and a pavilion for roller skating and special events. Includes news and flora and fauna lists.

Capitol Hill Parks - Provides urban green space for relaxation, aesthetic enjoyment and historic commemoration. Includes Lincoln, Folger, Stanton and Marion Parks as well as several medians, squares and triangles.

Chesapeake & Ohio Canal National Historical Park - Follows the route of the Potomac River from the District to Cumberland, Maryland. Includes original structures, including locks, lock houses and aqueducts. Features educational activities, information for children, news and history.

Fort Dupont Park - Named for the Civil War earthwork located within the park, offering picnic areas, nature walks, Civil War programs, gardening, environmental education, music, skating, sports and youth programs.

A History of National Capital Parks - This 1953 book by Cornelius W. Heine traces the history of the National Capital parks system since 1790. The text is accompanied by illustrations, tables and bibliography from the printed edition. From the National Park Service Web site.

Kenilworth Park & Aquatic Gardens - Includes the gardens, Kenilworth Marsh, ballfields and recreational facilities. Features a satellite program, preschool stories and driving directions.

National Mall - This National Park Service site provides a historical overview of how the National Mall has evolved since 1790, illustrated by a timeline chart. It also has lots of facts and figures about major Mall monuments and memorials, links to monument Web sites and a calendar of events.

President's Park South - Located on the south end of the White House grounds and generally known as The Ellipse. Includes activities and history.

Rock Creek Park - Includes the Nature Center, Planetarium Visitor Center, Old Stone House and Pierce Barn. Includes history, activities, educational programs and information for children.

Washington Parks and People - Non-profit organization dedicated to restoring and enhancing public parks in the National Capital Region. Information on programs, getting involved, events, and special features devoted to Meridian Hill/Malcolm X Park and Watts Branch Park, including photos.

Audubon Society of the District of Columbia - Field trips, events, birding around D.C., Logan Meadow sanctuary and newsletter articles.

Biodiversity Database of the Washington, D.C., Area - Searchable database of information and images. Includes organisms and regional nature and preservation areas in the D.C. area.

Capital River Relief - Coaltion of organizations and individuals focused on cleaning up the Anacostia and Potomac Rivers. Features cleanup schedule, photo gallery, press kit, and FAQs.

Casey Trees Endowment Fund - A project to restore the tree canopy of Washington, DC, administered by the Garden Clubs of America. Includes a review of the street tree inventory carried out in 2002.

DC Department of Health - Environmental Health Administration - Works to prevent and control environmentally related diseases while protecting and preserving the ecological system in the district. Features a guide to the bureaus and divisions that make up the Administration.

DC Energy Office - Promotes energy efficiency through conservation, education, and fuel assistance programs and by regulatory intervention. Includes consumer information, a description of agency programs, a guide to resources in its library, an events calendar, and links to related sites.

DC Greenworks - Non-profit organization supports projects and provides information on low-impact storm water management and urban forestry. Includes information on green roofs, rain gardens, and tree care.

Earthjustice - Washington DC - Focused on ensuring that national clean water and clean air standards are properly set and enforced in the District. Features urgent cases, opportunities for action, legislative information, news and campaigns.

Earthquake History of the District of Columbia - Seismic history of DC from the National Earthquake Information Center.

Environmentors - Committed to helping one hundred public high school students create opportunities for brighter futures through mentorship, educational enrichment, and the fostering of a sense of environmental stewardship.

Flora of the Washington-Baltimore Area - Offers information about flora native to the area. Includes a specimen database, projects, spring flowering records and a gallery.

Friends of the Earth DC Environmental Network - A consortium of conservation organizations that meets regularly to focus on environmental problems specific to the region, exchange information, and coordinate strategies. Includes background documents [PDF].

Hardy Palm Trees and Ferns - Showcases plants that can survive the area's often snowy winters.

HowStuffWorks: Exploding Manholes - Information on the frequent mishaps under the streets of the city.

Maryland-National Capital Park and Planning Commission - Acquires, develops, maintains and administers a regional system of parks in Montgomery and Prince George's Counties in Maryland.

The Nature Conservancy - Maryland/District of Columbia - Works to protect critical natural lands. Features places protected, events, news and volunteer opportunities.

Pre-Columbian Society of Washington, DC - Promotes interest in Pre-Columbian cultures through annual symposia, monthly meetings, and a newsletter. Includes newsletter index.

Sustainable Washington Alliance - Network of individuals, businesses, and organizations working to create a sustainable future for the region.

Trash Force - Volunteer group that picks up trash and recyclables from public areas every other weekend. Features FAQ, news, awards, volunteer opportunities and articles.

Urban Land Institute - Non-profit research and education organization focusing on the use of land to enhance the environment.

Washington Regional Network for Livable Communities - Advocates "smart-growth" transportation investments, land use policies, and community designs. Includes newsletter archive and policy documents.