Two of the rivers that flow through Wilton, the Norwalk River and the Saugatuck River, have come up clean in their annual monitoring for various forms of bacteria that could indicate raw sewage pollution.\u201cWe do monitoring in the Wilton section of these rivers year-round, and we\u2019re currently monitoring three sites for bacteria, and just wrapping up the final report in the next couple of weeks. We\u2019ll have more to say but it looks good,\u201d said Sarah Crosby, director of Harbor Watch, a water quality research and education program serving Fairfield County based in Westport at Earthplace.There are 11 river systems in Fairfield County that were monitored this summer. Each has several stations that are monitored twice a month, from May through September.\u201cWhat we\u2019re looking for is indicator bacteria, focusing on e-coli and fecal coliform bacteria, because that is an indicator of the presence of sewage pollution,\u201d Crosby said. If bacteria is discovered, teams of volunteers comb the river to find the source of the sewage and work with the town to get the problem fixed.\u201cWe didn\u2019t see any stations in Wilton of concern for bacteria. We won\u2019t make recommendations for further investigation until the full season is over, but overall things are looking reasonably good,\u201d she said.Ridgefield, which is up river on the Norwalk River, had a slightly different season.Of the 30 samples taken at the six Ridgefield sites, there were five that showed coliform counts above the state\u2019s criteria for \u201cpotential human health risk\u201d of 576 colony-forming units per 100 milliliters (576 CFU\/100mL) set by the Connecticut Department of Energy and Environmental Protection (CT DEEP).\u201cWhen we see a single high count, it isn\u2019t cause for concern,\u201d said Crosby, \u201cIt\u2019s more a systemic situation where we have elevated counts for multiple sampling dates.\u201cA single water sample could be influenced by any number of environmental factors, so it\u2019s really about having a number of replicates over a course of the season,\u201d Crosby said.Ridgefield\u2019s two sewage treatment plants discharge effluent into the Norwalk River: District 1 into the Great Swamp off South Street, and District 2 off Route 7 near Little Pond.One of the Harbor Watch testing sites is at the effluent discharge from the District 1 plant.\u201cFrom April to October, the plant has UV (ultraviolet) lights on to sanitize the effluent which results in no bacteria entering the Norwalk River from the treatment plant,\u201d the Harbor Watch report says. The organization has asked Ridgefield to run the lights in the winter as well.Coliform bacteria are commonly found in the intestines of people and warm-blooded animals, so they can be used as a marker to detect leaky septic systems or poorly functioning sewage treatment plants. But the bacteria also occur naturally, and there could be a number of causes \u2014 including geese \u2014 behind a coliform count over the state\u2019s 576 CFU\/100mL on an isolated occasion in water at a given site.