JEFFERSON CITY, Mo. — Gov. Jay Nixon fired a longtime aide and reinstated Missouri’s environmental chief Friday while announcing that an investigation revealed repeated state failures to protect the public from contaminated waterways.

Nixon took responsibility for poor decisions and communication within his administration, but asserted that Missouri’s Department of Natural Resources has “long-standing, institutional problems with the handling of water quality issues.”

An internal review found 10 cases over the past three years — half of which occurred this year — in which public beaches at state parks were not closed despite high E. coli levels, Nixon said. In 14 other cases since 2005, the DNR apparently kept quiet that high fecal coliform bacteria levels existed in the Lake of the Ozarks, Nixon said.

“For years, the department has ignored and failed to inform the public of troubling water sampling results. But for the first time, people are being held accountable,” said Nixon, a Democrat who took office in January.

The governor announced he is rescinding the appointment of Joe Bindbeutel to the state Administrative Hearing Commission, because Bindbeutel was “the chief decision-maker” in delaying the release of E. coli test results earlier this year when he was deputy director of the Department of Natural Resources. There already was doubt Bindbeutel could win confirmation from the Legislature.

But Nixon said DNR Director Mark Templeton would be reinstated to his job next week after being suspended for more than two weeks without pay.

“Mark has served a just punishment,” Nixon said. “He has faced reproach from the public and the press. He has spoken at length about his own failings on this matter, he has paid a price for the department’s mistakes.”

Nixon’s administration has been under fire since July 16, when The Kansas City Star revealed the DNR had waited until late June to release results from a May water quality test showing high E. coli levels in numerous parts of the Lake of the Ozarks.