The pedestrian and bicycle overpass at the north end of Aquatic Park in Berkeley. Photo: Emilie Raguso

The city of Berkeley is stepping up efforts to determine why dangerous bacteria that may cause illness have been proliferating in Aquatic Park since early August, making the park off-limits for recreation in recent weeks.

The latest available test results for enterococci bacteria in the man-made lagoon, from samples taken Sept. 23, showed more than 2,400 MPN/100 milliliters at the north end of the park, about 1,700 MPN at the south end and about 387 MPN (which stands for “most probable number”) in the middle. The safe threshold for a single enterococci sample is 104 MPN.

The enterococci numbers at the north and south ends of the park were up significantly from the prior week’s test results, when they were 370 and 520, respectively. City spokesman Matthai Chakko said the city’s advice about the water has not changed: Avoid all contact with it because it could cause illness.

In September, following discussions with the State Water Resources Control Board and other local water experts, the city began testing for enterococci bacteria for the first time in its history. Experts say that’s now considered the best indicator of safety for marine recreational water. The city is contracting with a private lab, Alpha Analytical Laboratories in Livermore, for those tests.

Historically, the city has tested the water in Aquatic Park for other bacteria levels monthly from May through August. This August, when E. coli bacteria levels first spiked, the city began a weekly testing protocol, with the Alameda County Public Health Laboratory, which continues. E. coli and other fecal bacteria levels did drop at one point, but went back up in September.

The most recent E. coli tests, also from Sept. 23, came in at 200 colony-forming units for samples taken from all three areas of the lagoon. That number is within the safe threshold — of 235 CFU or below per 100 milliliters — for a single sample. The city and water experts say a six-week mean is a more robust number to use, however, and that calculation has not been available to date. The city plans to do that analysis in the future as part of its ongoing testing, Chakko said.

In addition to increased testing, the city is also using dye tests at the lagoon to try to figure out where the bacteria are coming from, Chakko said, “to see if we can get a better understanding of what’s causing this problem.” He said the city is currently working to choose a consultant to carry out this analysis.

Update: The city will “dye test” significant entry points into Aquatic Park to determine potential sources of the bacteria spike in the lagoon. Weekly testing will continue. Berkeleyside has been following the story: #berkmtg— Berkeleyside (@berkeleyside) September 25, 2019

Some community members have said the city needs to do more, as it attempts to figure out what’s going on, to be transparent.

Isabelle Gaston said she called the city’s Environmental Health department to find out about recent test results, but no one got back to her. Other agencies that oversee recreational bodies of water, such as the East Bay Regional Park District, post water quality results online, she noted. Why isn’t Berkeley doing the same?

Chakko, the city spokesman, said he could look into whether that might be possible.

Elaine Baden, president of the Berkeley Paddling and Rowing Club, told Berkeleyside on Friday that the city has been less forthcoming with test results recently than it had been previously. Staff did not share the Sept. 23 results with the paddling group, she said, members of which were the first in the community to identify the problem, document it and alert the city to it.

Baden said she’s also concerned about whether the city is doing all it needs to do to solve the problem.

“They’re doing a lot of tests — but with no plan,” she said. “It doesn’t seem as though they’re looking in the right place.”

Baden said the city had floated one theory about rain causing the bacteria increase, as well as the possibility of RV dumping contributing to the problem.

But that doesn’t account for large amounts of water that have been flowing into the lagoon, she said. A number of the paddlers in the group have used the lagoon on a regular basis for many years and are familiar with inflows that are normal — as well as those that are not.

The first inflow, which happened in early August, caused a 10-inch or so increase in the water level over a single weekend, she said. Later in the month, a paddler recorded video of water coming into the lagoon again. There was another mysterious inflow in September, said Baden.

Baden said she’d heard, anecdotally, that recent dye tests had found no sewage leaks. The city was not available Friday to comment.

Baden’s working theory is that there’s some type of construction project happening in Berkeley that might be dewatering a site, emptying a storm drain so work can be done underground. If a sewage line is being emptied into the storm drain as part of the dewatering, she said, that could potentially account for what’s going on.

Chakko said earlier this week that the city has posted 20 signs around Aquatic Park telling people to avoid contact with the water because bacteria levels are “still considerably over the threshold.”

The city is also posting basic information on the Aquatic Park page on the city website.

“Avoid contact with the water at Aquatic Park,” the current alert reads. “Testing received on Sept. 27, 2019 shows elevated levels of bacteria. Water contact may cause illness. Shower and towel dry after contact. The City has increased its frequency of water sampling and is closely monitoring water quality.”

The city has been working with the water board, the park district and other agencies to try to figure out what’s going on, Chakko said. That includes looking at the tide tubes between the lagoon and the San Francisco Bay to try to figure out how to address the longstanding maintenance problem they pose. Chakko said that conversation involves the San Francisco Bay Conservation and Development Commission, Caltrans and possibly the U.S. Army Corps of Engineers.

Chakko noted that about a dozen storm drains, along with Strawberry Creek, flow into Aquatic Park. When it rains, there’s also runoff from Interstate 80.

“It’s not a natural body of water,” he said.

Emilie Raguso (former senior editor, news) joined Berkeleyside in 2012 and covered politics, public safety and development until her departure in 2022. In 2017, Emilie was named Journalist of the Year...