The report by Ecotago, ''unveiled'' last weekend, contains measurements of algae, E. coli, turbidity, nitrogen and phosphorus in the water body.
The project began three years ago and uses local schools, supervised by scientists, to measure the environmental health of the lagoon.
Ecotago scientist Andrew Innes said the study had enough information recently to release a ''report card''.
''I think, overall, the water quality at Tomahawk Lagoon I would categorise as poor.''
The study was needed because the Otago Regional Council had no regular monitoring scheme in the lagoon.
''We saw there was a place for us to do a bit of good science at Tomahawk Lagoon by teaching school groups about measuring its health.''
He was ''really pleased'' by recent consultation the regional council held with the community about its future.
The group receives funding from various sources, including the regional council's Eco Fund.
Regional councillor Andrew Noone said it was ''absolutely'' pushing to do more work on the lagoon.
''Clearly, in its current state, it's unacceptable to that community. We accept that. It will take some time, but we have the same focus as the community and other stakeholders about improving the water quality in that lagoon.''
The council was constantly trying to expand its monitoring network as the budget allowed, so a monitoring scheme at the lagoon was ''potentially'' on the radar.
