BROCKTON – For months, the state has discouraged people – and their pets – from coming into contact with the water at West Monponsett Pond.



The pond, in Halifax and Hanson, serves as one of Brockton’s drinking water sources. Tests performed by the Department of Public Health going back to June have shown excessive levels of cyanobacteria, a poisonous algae that can be harmful to humans and animals at high concentrations.



Last Monday, the pond tested well above state safety limits in three places, including more than twice the limit in two places.



That same day, the Brockton Water Department began diverting hundreds of millions of gallons of water from the pond into Silver Lake, the city’s chief drinking water supply and where water is treated before being sent into thousands of homes and businesses.



“This is a public health issue,” said Kate Archard, a member of the city’s Water Commission. “You’re taking polluted water and putting it into clean water. Why would you take a pristine source and dump crap into it?”



Regional water experts are questioning the recent diversion of water – 183 million gallons and counting – not because it is illegal or even out of the ordinary, but because the amount of contaminated water involved poses questions they say Brockton officials have not answered.



The Central Plymouth County Water District Commission, charged by law with managing water use in the region, has requested that Brockton present evidence from a professional engineer that the diversion is not creating public health or environmental problems.



“We don’t know if it’s a hazard,” said Paul Collis, an attorney from Halifax and member of the commission. “We just want some assurance that it isn’t. We’d like to hear from Brockton that they can allay our concerns with evidence.”



The diversion will not have an adverse affect on the quality of drinking water, according to Brian Creedon, the city’s water systems manager. He said he plans to speak with the commission about the issue at its meeting Tuesday, although he said he does not plan to enlist an independent engineer to assess the risks.



He said that DPH water testing showed Silver Lake was within acceptable limits for cyanobacteria last Monday, although that was before the millions of gallons were diverted into the lake.



In 1899, the state Legislature allowed the city to tap Silver Lake, a 640-acre lake in Pembroke, Kingston and Plympton. A 1964 law subsequently allowed Brockton to move water from West Monponsett Pond and East Monponsett Pond into Silver Lake from October through May to control water levels.



Silver Lake contains 5.1 billion gallons of water, according to a report issued by the Town of Halifax in July 2013. East Monponsett Pond and West Monponsett Pond together contain 1.2 billion gallons of water.



Creedon said the water Brockton is diverting actually flows from East Monponsett Pond into Silver Lake. That pond tested below acceptable levels last Monday and has not been under a state advisory since Oct. 2.



However, Collis said that even though the water technically enters Silver Lake through East Monponsett Pond, it comes from a pipe connected to West Monponsett Pond. He has also asked that cyanobacteria be tested at the connection area of both ponds.



The commission Collis sits on was founded 50 years ago to manage the region’s water problems. It was reconstituted last spring and funded with a $50,000 state appropriation.



Since then, however, neither the commission nor an associated advisory board have had representatives from Brockton. Two are missing from the advisory board and one from the commission.



Brockton Mayor Bill Carpenter said he has not appointed Brockton representatives because he has been waiting for a permanent DPW commissioner to take over following Michael Thoreson’s retirement earlier this year. That selection process is ongoing, he said.



“We’re not blind to it,” Carpenter said. “We have had some internal discussions. I’m well aware of the need.”



Ossie Jordan, chair of the city’s Water Commission, did not respond to a request for comment.



Joseph Markman may be reached at jmarkman@enterprisenews.com.



