A large area of Charlottetown Harbour has been closed to shellfishing because runoff caused raw sewage to be released into the water last weekend.

It means some oyster fishermen will have to find somewhere else to fish as the season begins this week. Stan Casey was hoping to fish in Charlottetown Harbour on Thursday, but that won’t happen.

"With all the runoff into the sewer system, we had an overflow. Shut down our fishing in some areas," he said.

Areas of Charlottetown Harbour that are near sewage outflows haven’t been open to shellfishing for years. But there are other areas that are supposed to be safe.

The city says it's about halfway through the job of separating the combined sewage and storm systems, which will improve the situation. The work is expected to be completed by 2015.

Even so, sewage from the treatment plant could still end up in the harbour, depending on the amount of rain and snow that falls.

"The risk is still there with that, but definitely we should see less and less as time goes by," said Craig Walker, Charlottetown’s utility manager.

Casey said about 50 people will be affected by the closure. They'll have to travel further afield to fish, putting more pressure on oyster stocks in those rivers.

"We want to make sure that our oysters are safe and we want to keep that reputation of being the best in the world," Casey said. "And this is the way we do it."