Hurricane Irene's heavy rains, forecast for Southwestern Connecticut Sunday, will strain the region's sewer systems and lead to additional pollution in Long Island Sound.

"Under the best of times, with normal rain patterns and things, we struggle with rainwater runoff," said Terry Backer, a Long Island soundkeeper with Soundkeeper, Inc. "Under these types of projected rains, there is nothing you can do."

The director of the state's Aquaculture Division said he was confident the coastal sewer systems will be able to handle the deluge, and was more concerned that massive power outages could take sewage treatment plants offline.

All the pollution in a storm water system tends to get flushed out with just one to one-and-a-half inches of rain, said Leah Schmalz, director of Legislative and Legal Affairs for Save the Sound, and the rest of the water exiting the pipes is clear rain water.

"It's important to remember we have every contaminant we can think of -- PVs, oil, debris from highways. All that will be flushed out in the first hour of rain," Backer said. "We call that the first flush. We've worked on ways to try to deal with that for years. There are some ways, but they're very expensive."

But in Bridgeport and New Haven, cities that still are predominantly served by old systems in which sewage pipes and storm water pipes are combined, it takes less than an inch of rain to inundate the system and cause sewage overflows. Bridgeport's system typically overflows after a half an inch of rain, while New Haven's system floods after about an inch of rain. More rains will prolong flooding, causing more sewage to flow directly into the Sound, Schmalz said.

"The sewage issue is a real one," Schmalz said. "A lot of water will be running through the system and all of that will be running into the Sound."