• Corporate Wetlands Restoration Partnership
• Ducks Unlimited
• Eight Towns and the Bay
• Essex County Forum
• Essex County Greenbelt Association
• Essex County Trail Association
• Essex National Heritage Commission
• Great Marsh Coalition
• Ipswich River Watershed Association
• Massachusetts Audubon Society
• Merrimack Valley Planning Commission
• Metropolitan Area Planning Council
• The Nature Conservancy
• Parker River Clean Water Association
• Salem Sound Coast Watch
• The Trustees of Reservations
• Trout Unlimited

Federal Government

• Army Corps of Engineers
• Environmental Protection Agency
• Fish and Wildlife Service (Partners for Fish and Wildlife)
• National Marine Fisheries Service
• NOAA Restoration Center
• Natural Resources Conservation Service
• Parker River National Wildlife Refuge

State Government

• Department of Conservation and Recreation
  -ACEC Program
  -Lakes and Ponds Program
• Department of Environmental Protection
  -Wetlands Protection
  -Stormwater Management
• Department of Fish and Game
  -Riverways Program
  -Division of Marine Fisheries
  --Survey of Anadramous Fish Passage (incl. North Shore)
• Office of Coastal Zone Management
  -Wetlands Restoration Program
• Massachusetts Bays Program
• Natural Resources Damages Program
• Northeast MA Mosquito Control & Wetlands Mgmt. Dist.
  
  Local Government
• Town of Essex
• City of Gloucester
• Town of Ipswich
• Town of Newbury
• Town of Newburyport
• Town of Rockport
• Town of Rowley
• Town of Salisbury

The Great Marsh Coalition has compiled a list of publications on the natural history of the Great Marsh.

We've tried to compile relevant resources, but it is impossible to identify them all, so please let us know of others we should consider adding.