American Water Gardening Society
Forums include general pond chat, galleries, and plant exchange.
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
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.