A leading water expert says conditions have been too inconsistent to tell if Cantabrians are cleaning up rivers and lakes.

Professor Jenny Webster-Brown's comments come after Environment Canterbury released its annual Freshwater Quality Report.

It said waterways have improved, but just under a quarter are still unswimmable.

Professor Webster-Brown said we need more data before we take credit for helping Canterbury waterways.

"It's probably far too soon to say that the actions that have been taken over the last little while are making a difference because there is a huge amount of variability in the data from year to year."

She said this year's improvements might just reflect the end of the drought.

However, she said that at least the reports do mean swimmable when they say swimmable.

"[The results are] based very stringently on Ministry of Health and Ministry for the Environment recommendations on what should be used to some ability. I think they are remaining very rigorous."

The release of the report has resurrected calls for an upheaval of the regional council structure.

One of Labour's election promises was to restore full democracy to E-Can.

Six Government appointees have been part of the Council since locally elected representatives were sacked in 2010.

Water activist and author Sam Mahon said Cantabrians won't be fully satisfied with ECan's work until the Government appointees are gone.

"It's all very possible that the people that are elected could be pro-development. I don't really care about that because the principle here is to have a democratic Council."