From swimming to pleasure boating to Seafair, Lake Washington has a lot to offer in the summer. Do you ever think, though, before you jump in, about what else ends up in water so surrounded by urban development?

Though Lake Washington’s health has improved dramatically since the 1940s-’60s when Seattle’s sewers flowed into it, budget cuts for water quality monitoring programs combined with pollution from storm water drains, sewer overflows, fertilizers, animals and contaminated urban streams continue to complicate state, county and Mercer Island cleanup efforts, according to environmental workers.

Public concern about water quality in the Seattle area has grown over the last 40 years or so, according to Sandy Howard of the Washington Department of Ecology, which is responsible for enforcing environmental protection rules in the state. With the help of federal laws like the Clean Water Act, she said, the department has become much more effective at regulating water pollution from industry, but non-point pollution sources like urban runoff make regulating what goes into the lake a difficult endeavor to this day.

“Our biggest challenge right now is storm water and the things people do on land,” said Howard. “Things like that end up in the lowest place, which is the big bathtub of Lake Washington and Puget Sound.”

Based on data from the county’s mid-lake station in Lake Washington, overall water quality in the lake is good, but close to shore in some places, higher levels of phosphorous have led to algae growth, said Debra Bouchard, King County Water Quality Planner. She said lake quality is measured using a system called the Trophic State Index, which is designed to tell whether harmful algae blooms are likely.

Brooks Miner, a PhD student who studies lakes in the University of Washington biology department, said Lake Washington was an encouraging example of the way that scientific studies could trigger public concern and eventual policy action on environmental problems. In the 1960s, he said, a professor at the UW named Tommy Edmondson was instrumental in getting city sewers diverted from the lake.

“The current status of Lake Washington is one of the cleanest urban lakes in the world,” Miner said. “It’s a kind of neat success story.”

Part of the reason it cleaned up so quickly, Miner said, was because Lake Washington has what scientists call a short water residence time, meaning water cycles through the lake quickly before leaving through the Ballard Locks.

Dean Wilson, also a Water Quality Planner for King County, said he tracks water quality at swimming beaches on the lake, checking for fecal coliform and toxic algae, which can indicate that the water may be harmful to humans. He’s found, he said, that streams and storm water runoff tend to carry pollutants into the lake and sewer overflows, pets and geese can cause problems as well.

Of the beaches that he monitors, Wilson said Luther Burbank Park on Mercer Island is one of the cleanest thanks to a current that runs up the east side of the Island from the Cedar River, Lake Washington’s main water source.

“There’s never been any problem there,” he said of Luther Burbank. “It’s a great beach to swim at.”

Beaches that have higher concentrations of bacteria, he said, tend to be those that have urban streams feed into the lake nearby. He said Matthews Beach in Seattle is an example.

According to the King County water quality Web site, 2008-09 testing data showed that 84 percent of the urban stream sites monitored in the Seattle area had poor to moderate water quality. One of the worst was Thornton Creek, the outlet of which is near Matthews Beach.

Due to budget cuts, however, the county reported that its water quality monitoring program was reduced in 2009. According to its Web site fewer than half as many streams were monitored in 2009 as before. Bouchard said many of the data sets at stream sites that were abandoned went back to the 1970s.

In the lake itself, fecal coliform testing in areas away from swimming beaches was abandoned, according to the county Web site, and Bouchard said overall testing sites in Lake Washington were reduced from 13 to four. She said she had been told there could be more cuts to the county’s freshwater monitoring program in 2011.

Besides pollution problems from streams, Wilson said the county had also found higher levels of fecal coliform at beaches with dog parks, but when officials returned to retest areas like the off-leash area in Magnuson Park, Seattle, they often found bacteria levels had returned to normal.

If high concentrations of fecal coliform are detected at a beach, Wilson said, the area is retested. Then, the county notifies public health, which advises the beach manager, who is responsible for deciding whether the beach will be closed.

Wilson said the county uses a fecal coliform level agreed to by the Washington Health Department and King County Public Health as its standard for deciding whether a beach should be closed. The King County water quality Web site said no standard measure for water quality and no protocol for actually closing swimming beaches has been provided by the state.

The City of Mercer Island was also participating in water quality monitoring in the Lake Washington area, according to City Engineer Patrick Yamashita.

He said Mercer Island has been paying King County staff to monitor about six streams around the Island since 1999. Overall, he said, the results have been similar to those in the rest of the Seattle area.

Thanks to the monitoring program, though, he said the city had been able to establish that erosion control measures they had enacted were reducing sediment in the water and pesticide bans were leading to fewer chemicals in Island streams.

Like the rest of King County, Yamashita said, Mercer Island has been struggling with storm water runoff. In response, he said the city maintenance department was trying a new technique in drainage ditches called bioswale, which uses vegetation like grass to better filter storm water.

Howard said there are lots of small things people in the Seattle area can do to protect the lake.

“Lake Washington is a huge lake so you probably don’t think little things you do matter, but everything has a downstream impact,” she said.

She recommended picking up after dogs, washing cars so that the soapy water doesn’t run into storm drains and using public transit because cars add pollution to the lake through old copper brake pads, for instance.

Both Howard and Wilson said boaters could make a difference by being careful at fuel docks and by not dumping holding tanks into the lake illegally during events like Seafair.

“You’re never going to get it back to the way it was before people started living here and building houses and paving roads,” said Howard of Lake Washington.

One reason to be hopeful, though, is that things have improved significantly over the last 50 years, when sewers ran into the lake and problems like urban runoff did not make it onto the policy agenda.

“It’s pretty amazing that’s how it used to be,” said Howard. “As a society, we’ve come a long way toward protecting our water.”