Peter Langlands visited the lake over the weekend. He took photos of pied oystercatchers feeding on the mussels.
Lake Heron is one of the lakes at Ōtūwharekai Ashburton Lakes.
Langlands said the lakes currently have low levels, most likely due to a lack of rainfall.
The level at Lake Heron was about 0.5m lower than normal, and Langlands said it was the lowest level he has seen since he started visiting the area in the 1980s.
He has seen a similar event, in which freshwater mussels died off due to low levels, at a North Canterbury high country lake in the early 2000s.
Langlands is also concerned about the water quality of Lake Heron.
It was recently graded as poor by Land Air Water Aotearoa.
"It’s such a special place up there, it’s heartbreaking to see how that lake has gone in the last few years," Langlands said.
He also saw evidence of cattle grazing around the lake edge during his visit over the weekend. He reported this to Environment Canterbury.
However, acting manager compliance Jennifer Rochford said ECan visited the lake in response to Langlands’ complaint but found "no evidence of pugging or cattle near the lake edge".
Meanwhile, a working group is creating a catchment plan to address declining water quality at Ōtūwharekai.
The Ōtūwharekaii Working Group is made up of representatives from ECan, government departments, local farmers, runanga, the Ashburton District Council and Fish and Game NZ.
