Together the groups represent 200,000 registered boat users (Boating Industry Association of Victoria), 840,000 recreational fishers and 138 fishing clubs (VR Fish), and 200,000 people concerned about the environment (Environment Victoria, Victorian National Parks Association).
The joint letter to the acting Victorian Water Minister Richard Wynne was also signed by local groups Goulburn Valley Environment Group and the Goulburn Valley Association of Angling Clubs.
The letter was drafted in reaction to a review into Goulburn inter-valley trade by DELWP.
The existing Goulburn IVT rules have allowed massive volumes of water through the river to downstream irrigators, resulting in bank and ecosystem damage.
The groups are collectively concerned the review being undertaken does not go far enough and will continue to allow unseasonably high IVT flows.
In the letter, the united groups say low and slow summer flows provide safe conditions for fishing, camping, swimming and boating.
More natural flows will also stop the erosion of banks, destruction of vegetation, inundation of sandbars and killing of young fish.
Boating Industry Association of Victoria chief executive Steve Walker said his organisation supported a variable flow level that doesn’t exceed an average 940 Ml per day over the peak irrigation period.
During recent years, 2700 Ml a day was being pushed down the river.
Environment Victoria Healthy Rivers campaigner Tyler Rotche said proposals for pulses of 2000 Ml and 6000 Ml per day weren’t acceptable.
“The Goulburn needs to be treated like a living river, not an irrigation channel,” Mr Rotche said.
GVEG president John Pettigrew said it was essential government understood people were still concerned about high flows in the Goulburn.
“I think it is important communities unite on issues like this; it's a heritage river but for locals it is more than that,” Mr Pettigrew said.
“In summer now you are lucky to find a sandbar to swim on. That's because of these high flows.”
The Goulburn holds the second-largest river population of Murray cod in Victoria.