Environmentalists filed a complaint Wednesday with state's inspector general over aerial spraying of insecticide to control mosquitoes carrying Eastern Equine Encephalitis (EEE).

The disease is rare, but can be deadly. There were 12 human cases in Massachusetts last year, six of which were fatal. Mosquitoes have already tested positive for EEE in two Massachusetts towns this year, officials said Tuesday.

The complaint, filed by the group Public Employees for Environmental Responsibility (PEER), says the spraying is both ineffective and harmful to human health and wildlife. The Jones River Watershed Association and the group LEAD for Pollinators also co-signed the complaint.

"We recently got the efficacy data from the state showing that the 2019 aerial spraying really didn't do anything," said Kyla Bennett, Science Policy Director for PEER. "And it was at a great cost, both monetarily and environmentally."

Bennett said the state sprayed six times last summer over the course of 26 days, covering more than 2 million acres.

"The last three sprays, which took place in September, were done, according to the state's own data, after there were no mosquitoes around because of the cool temperatures and they had zero percent efficacy," Bennett said.

Bennett said the chemicals used are carcinogenic and can suppress immune systems. The chemicals are also known to be harmful to bees and insects.

"So if they can't prove that this spraying is helping reduce this deadly disease and we do know that the spray is poison and bad for people and the environment, why are we doing it?" Bennett said.

In a statement Wednesday, a spokesperson for the state Department of Public Health said the Baker administration is using all available tools to fight the disease.

"Spraying is only one tool — and a rare one — the state uses when risk levels indicate an immediate threat to human life and health," the statement says. "Every effort is taken to safely deploy aerial application only in those places and times when it can have an impact on that risk without harming insect and fish species.”

State Public Health Commissioner Monica Bharel said Tuesday that mosquitoes have already tested positive for EEE in two Massachusetts towns, the earliest the virus has been detected in mosquitoes in the state in 20 years. No cases have been detected in humans or animals so far. Last year, Massachusetts saw a resurgence of cases, with more than 200 communities designated as moderate to critical risk by the state Department of Public Health. The state typically experiences outbreaks every 10 to 20 years. Each outbreak can last two to three years.

Mosquito control efforts like spraying are handled by regional partnership projects around the state. Those groups have been fighting mosquitoes since the spring, applying larvicide that target the mosquito species that spread the disease. Gov. Charlie Baker recentlyfiled legislation that would authorize a proactive statewide approach to mosquito control.

The Associated Press contributed to this report.