This warning sign was accompanied by a map, showing the closed area. Laura Chapin/CBC

The city of Charlottetown is working to fix the problem with the sewage system that kept oyster fishermen off the water Thursday, Mayor Clifford Lee said.

"We're not sitting back doing nothing. We're trying to come up with a solution," he said. "The reality is it's a $20 million problem and we need assistance from the other two levels of government to solve the problem."

Environment critic Jim Bagnall said the city should have made the sewage infrastructure a priority a long time ago, and now the province should start fining the city for polluting the harbour.

"Maybe if they had fined the city of Charlottetown 10 years ago when this problem started happening, and every time, then it would have become a priority for the city," Bagnall said.

"But if you continue to do it without any penalty and without anything happening, you're going to continue to do it."

Lee said he will meet with Environment Minister Richard Brown next week to discuss the project, and then they'll have to ask Ottawa for some funding.

Charlottetown harbour and sections of the North, West and Hillsborough rivers, along with Hillsborough Bay were closed Wednesday to shellfish harvesting due to another spill of sewage water from the city.

Fisherman Ellery Pitt is frustrated by the sewage troubles that have closed Charlottetown harbour to oyster fishing. (CBC)"They're shutting everything down and making it harder for us to find spots to fish," fisherman Ellery Pitt said.

"They made us sign a paper that you can't urinate in the water, and they're dumping in everything from the Charlottetown sewer."

Bill Drost, of the Department of Fisheries and Oceans, said it's a frustrating situation.

"It's certainly an issue that frustrates us from time to time as well, because we have to close the areas, ask fishers to dump shellfish that they may have in their possession and then go back and open the areas again," he said.

Gilbert Gillis , who fishes the North River, told CBC News Thursday that the upper reaches of the river are under more pressure lately because they usually don't close.

"The quality seems to be down, the amount is down, the volume, and it's not producing," said Gillis. "We just have to go where we're allowed to go and that's putting us in places that are not so productive."

The closures happen because part of Charlottetown's sanitary and storm sewer systems are combined, meaning heavy rains can overflow the treatment plant.

There have been 17 closures due to sewer overflows in the last couple of years. The most recent was late last month on the eve of the start of oyster season.