Fish and Game are calling for action, following the rapid decline of the Invercargill Estuary.
A report prepared by Environment Southland, shows the amount of macro algae in the estuary, had increased substantially over the last 20 years.
"Twenty years ago there was about 20 hectares of this sort of degraded habitat within this part of the estuary ... and now it’s over 400 hectares," Fish and Game Southland manager Zane Moss says.
Mr Moss puts the decline down to intensive dairy farming, saying the run-off from farms in to rivers is of real concern.
Federated Farmers Southland President Geoffrey Young disputes that claim though, saying the contaminants come from several other urban factors and that farmers in the region are farming sensibly.
Michael Skerett, whose family grew up in the region, says he’s saddened when he looks at the site, a place his family used to gather seafood and swim in.
"It's really frustrating, it was such a great recreational area. But I’m not going to go dipping my head in there or harvesting food anymore... it’s a really sad thing," he says.
Fish and Game say a full clean-up is not really an option right now, citing the immediate focus is to just stop it getting worse.