An environmental watchdog group has filed lawsuits against the cities of Mountain View and Sunnyvale alleging that the cities' aging sewer systems are leaking bacteria from human feces into stormwater drainage systems, contaminating local creeks and ultimately the Bay.

Over the past few rainy seasons, San Francisco Baykeeper, a nonprofit that works to protect the Bay and its water quality, has sent scientists to measure the amounts of various bacteria that indicate the presence of human fecal waste. In some instances along Stevens Creek, the nonprofit found levels of those bacteria about 50 times higher the legal limits, Baykeeper reported on its blog.

The Mountain View suit alleges that the city's old sewage system, mostly made up of breakable clay pipes, has leaks that have released bacteria found in human feces into the city's stormwater drainage system. From that system, the bacteria are being discharged into Stevens Creek and other bodies of water that feed into the Bay.

The pollution has been going since at least 2014, according to a state study that identified the water as polluted, said Sejal Choksi-Chugh, Baykeeper's executive director.

Eighty-nine percent of the sewage system is made up of clay pipes, which are susceptible to cracking and breaking, the suit claims. The sewage system is also aging: at least 26% of it is more than 60 years old, and at least 57% is more than 20 years old. More than a third of the system doesn't have a recorded age.

"Many of the two cities' older clay sewer pipes are cracked and probably leaking raw sewage into the stormwater pipes. The cities also have inadequate urban pollution controls, so that contaminants flow freely from streets into storm drains," the Baykeeper blog alleged.

Since the suits were filed last month, the cities have gotten in touch with Baykeeper, Choksi-Chugh said.

"Baykeeper is in conversation with Mountain View and Sunnyvale right now, and it's clear they want to do the right thing for their residents. We think things will go smoothly -- nobody wants to waste a lot of time in court!" Choksi-Chugh told the Mountain View Voice in an email.

The city of Mountain View is exploring steps to resolve the allegations, according to city spokesperson Shonda Ranson.

"The city of Mountain View is committed to the protection of the public's health, safety and welfare and the safe condition of local creeks. The city is carefully reviewing Baykeeper's allegations while continuing to meet with them and keeping an open dialogue. We are evaluating next steps with the goal of a timely and appropriate resolution," she said in a statement.

The ability for bacteria-laden water to enter local waterways is a common problem, said Lisa Horowitz McCann, an officer from the California Water Board's San Francisco Bay regional office. In particular, old sewer systems overflow when there are blockages in dry weather and capacity constraints in wet weather.

Such contamination events can lead to people being exposed to the bacteria, which can make them sick. The Bay is heavily used for recreational purposes, and people may be exposed through activities like swimming, kayaking, stand up paddleboarding and windsurfing.

The presence of raw sewage in local waters also poses a health risk to anyone who might eat fish caught in those streams. "Contaminated fish are particularly damaging to ethnic and economic minority communities, who eat a greater-than-average amount of locally caught fish," the lawsuit claims.

Wildlife may also be impacted, but the risks to animals from human pathogens is lower than it is to other humans, McCann said.

Still, there are a number of endangered and protected species found along Stevens Creek and South San Francisco Bay that may be vulnerable to the contaminated water. The creek is one of the last remaining viable habitats for Central California Coast steelhead trout, and the creek's brackish reaches are home to the federally endangered California clapper rail and salt marsh harvest mouse, according to the lawsuit.

San Jose and other cities along the Bay have had similar problems to Mountain View and Sunnyvale, said Choksi-Chugh. San Jose is working on addressing its sewage pollution, she added.

While no illnesses have been directly attributed to the fecal bacteria, sometimes such incidents are not reported or people don't know that polluted water has made them sick, she said.

"Then you have to consider the very real damage additional pollutants will cause to the Bay's already compromised health. We know the level of risk is unacceptably high, so it's the cities' responsibility to act now," she said.