DC Nature
- Photo galleries of DC area wildlife created by a local group of nature photographers.
- http://www.dcnature.com/

Audubon Naturalist Society
- Independent conservation organization serving the Washington D.C. metropolitan region. Find programs, classes, current issues, news, and information about sanctuaries in Maryland and Virginia.
- http://www.audubonnaturalist.org/

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.
- http://persoon.si.edu/DCFlora/dcherbarium.htm

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.
- http://www.capitalriverrelief.org/

Audubon Society of the District of Columbia
- Field trips, events, birding around D.C., Logan Meadow sanctuary and newsletter articles.
- http://www.dcaudubon.org/

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
- http://www.dcenergy.org/

Urban Land Institute
- Non-profit research and education organization focusing on the use of land to enhance the environment.
- http://www.uli.org//AM/Template.cfm?Section=Home

Pre-Columbian Society of Washington, DC
- Promotes interest in Pre-Columbian cultures through annual symposia, monthly meetings, and a newsletter. Includes newsletter index.
- http://www.pcswdc.org/

Hardy Palm Trees and Ferns
- Showcases plants that can survive the area's often snowy winters.
- http://www.wap.atfreeweb.com/Palmdc/

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.
- http://www.dcgreenworks.org/

The Nature Conservancy - Maryland/District of Columbia
- Works to protect critical natural lands. Features places protected, events, news and volunteer opportunities.
- http://nature.org/wherewework/northamerica/states/maryland/

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.
- http://www.earthjustice.org/regional/washington_dc/

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.
- http://www.mncppc.org/

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].
- http://www.foe.org/camps/reg/dcen/

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.
- http://www.caseytrees.org/

Earthquake History of the District of Columbia
- Seismic history of DC from the National Earthquake Information Center.
- http://neic.usgs.gov/neis/states/district/district_history.html

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.
- http://biodiversity.georgetown.edu

HowStuffWorks: Exploding Manholes
- Information on the frequent mishaps under the streets of the city.
- http://www.howstuffworks.com/exploding-manhole.htm

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