Drowned rodents, parasites and pathogens: Lake Lag’s potential hazards

Since the start of the winter quarter, numerous students have visited the newly filled Lagunita Lake, with many walking past the university’s warning signs on their way to the water. But what mysteries lie beneath the murky waves of Lagunita?

Debris, parasites, aquatic pathogens and dead rodents can all inhabit the murky waters of Lake Lagunita, according to Stanford ecology experts, confirming previous university warnings advising students not to enter the lake. While the university only warned students about possible “debris, bacteria and deep mud,” experts said other contaminants could be plaguing Lake Lagunita’s murky waters.

“There’s definitely a lot of drowned rodents floating around,” said Alan Launer, director of Stanford Conservation Planning. “If the reservoir suddenly fills up, well, a lot of the resident rodents don’t make it and swim around for a while before they decompose.”

“My friends and I took a walk along the shore to count how many dead gophers there were,” Daily contributor Steven Liu ’26 said. “We walked about 100 meters and there were 30 dead gophers.”

(PHOTO: STEVEN LIU/The Stanford Daily)

In addition to decomposing mammals, experts warned students that there could be sharp objects in the lake. “For decades, people in Lagunita have been leaving trash, including glass,” Launer said. “As a result, there are some items in the reservoir bed that can cause large cuts.”

Launer also spoke about “swimmer’s itch,” a rash caused by parasites in the water. Launer, who dealt with the rash for about a month in the 1990s, described it as “red lumps that looked horrible and itchy.”

Elena Litchman, an ecologist at the Department of Global Ecology, believes swimmer’s itch is a “real possibility.”

“These parasites can swim underwater and then basically invade and burrow into human skin and cause this allergic reaction,” Litchman said of the rash.

Luckily, recent cold temperatures could protect students from the parasite. “Statistically anything is possible, but at this low temperature it’s probably not that big of a problem,” Litchman said. However, she advises students to remain cautious.

“Generally speaking, if it’s unfamiliar shallow water, you probably shouldn’t swim in it,” Litchman said.

Alexandria Boehm, a Stanford professor of civil and environmental engineering, agreed with Litchman.

According to Böhm, stormwater runoff often contains potentially dangerous pathogens, bacteria and eukaryotic organisms. “There’s a whole range of different pathogens that are present in animal feces and human sewage that can get into rainwater,” Böhm said.

“Swimming next to and in gullies leads to a higher risk of skin rashes, respiratory diseases and intestinal diseases such as diarrhea and vomiting,” Boehm said. “For the advice not to swim in rainwater, there’s definitely the scientific evidence base.”

While Boehm advises against entering the lake, she acknowledged that some students could still take the chance. “Everyone has a certain risk threshold,” said Böhm. “It’s how everyone decides what risk they’re willing to tolerate.” Many students will likely continue to enjoy the high water level before it slowly drains away.

“I wouldn’t swim in it, but I would dip my feet in it,” said Hayden Kwan ’26. “I wouldn’t dip my head under water.”

Some students seem to be more reserved.

“100% go to the lake to see the lake,” Liu said. “But don’t go into the lake, will you?”