The Parliamentary Commissioner for the Environment has labelled the government's new water quality targets as worthy but confusing.
Commissioner Jan Wright said there were "some good things" in the policy, including around stock exclusion.
"The document is largely a reaction to the public outcry about wadeability being a standard for freshwater, if you recall ... They have moved to a focus on swimmability. The government has taken on the message that people want to go down to a river on a hot day and jump in.
"Another thing they've done in it - they've got a map, with a colour scheme, that grades rivers in swimmability from blue to red, where blue is excellent and red is very bad. They've published all of those, and that's very transparent, and that's going to upset some of the councils."
On the bad side, Dr Wright said, the changes in water quality measurement were "very confusing".
"There have been some goalposts moved, or some ways of measuring things moved, and it's very difficult to tell whether things are being tightened or loosened. That's a big concern of mine."
The 90 percent target also included many waterways that no-one would swim in anyway, including rivers in very remote or very cold places, she said.
"It's where do people want to swim and at what time of the year ... There's sort of a dilution that's gone on by putting the whole length of these rivers in, and the whole areas of these lakes."
She said the focus should instead be on the most vulnerable, or already-polluted, areas, which tended to be closer to sea level and near where people lived.