Aquaria Central Forums: Discussion on many fish and aquarium topics, including a forum for indoor and outdoor ponds.
GardenWeb: Ponds & Aquatic Plants: Forum for discussion of design, construction and maintenance of ponds, and growing aquatic plants.
Hallson Gardens Forums: Bulletin board for gardening subjects, including one for ponds and bogs.
JB's Water Gardening Forum: This friendly, fairly active forum is open to all pond and water gardening topics.
Mississippi Wildlife Forums: Farm Pond Management Forum: Provides a moderated forum to discuss any aspect of managing farm ponds and small lakes.
PondHobbyist.com: An online community and resource center for pond and watergarden hobbyists. Forums, articles, links.