MORGAN HILL — On most sunny summer weekends, Coyote Lake, a 4-mile-long reservoir in the hills east of Morgan Hill, would be busy with people boating, water skiing and fishing for bass and blue gill.

But this Sunday, the boats were gone and the boat ramp was padlocked. Although camping and hiking at the county park are still allowed, the lake is closed for the rest of the year.

Water officials closed off the reservoir last Monday — nearly two months earlier than normal — after drawing the reservoir level down below the bottom of the boat ramp. Boating at nearby Anderson Reservoir could be shut down in a few weeks.

The reason: Santa Clara County needs the drinking water, and the region’s usual supply system has been disrupted by algae and lingering drought issues.

Normally at this time of year, the Santa Clara Valley Water District, a government agency that provides drinking water and flood protection to 1.9 million people in Santa Clara County, relies heavily on water from the Sacramento-San Joaquin River Delta for its supplies.

But this year, high levels of algae in the Delta, and also in San Luis Reservoir, a massive lake near Los Banos from which the water district draws some of its supply, began giving the water an earthy taste and smell in late June. So the district essentially closed off the pipe from San Luis and began taking more drinking water from Coyote Lake and Anderson Reservoir instead.

“Once we started getting complaints, we immediately switched to a different source, and that took care of it,” said Bruce Cabral, water quality manager for the district.

The water was always safe to drink, said Cabral, and it meets all federal and state health standards.

But the algae problem has caused the water district to scramble. In most years, water from Anderson and Coyote reservoirs is left in storage through the summer as an emergency backup source. It’s drawn down in late fall to provide room in the reservoirs for winter rains as a flood control measure.

Drawing the lakes down early, however, means boaters are taking the hit. On a typical Saturday or Sunday, Coyote Lake — which is now just 30 percent full, down from 50 percent on July 6 — gets about 50 to 60 boats, said Lachelle Ourricariet, a seasonal aide at the park. This Sunday, three turned up. Five arrived the day before.

“We’ve put signs up on the road,” she said. “Most people get it. They understand we are in a drought. But they say they are still bummed out because they drove all the way up here.”

Anderson on Sunday was 54 percent full. When it falls to 46 percent full, possibly by mid-August, the water level will be below the boat ramp, said James O’Brien, a senior engineer at the Santa Clara Valley Water District. Serving the water to drink also means that less will be put back in the ground to recharge aquifers than in typical years, he said.

The drought is playing some role. In rainy years, when big reservoirs and the Delta have more water in them, algae problems are few and far between.

This year, El Niño storms helped fill Northern California’s two largest reservoirs, Shasta and Oroville, for the first time in five years. But most of the rains came in March, at a time when endangered salmon, smelt and other fish were swimming by the huge state and federal pumps at Tracy that are used to move water from the Delta to San Luis Reservoir.

Biologists at the U.S. Fish and Wildlife Service and National Marine Fisheries Service told the state not to run the pumps at heavy rates. So San Luis reached 52 percent full by April 1, about half its historical average for that date.

Today, Shasta and Oroville are still 89 and 87 percent full, respectively, but San Luis has been drawn down so steadily by cities and farms that it sits at just 11 percent full, a breeding ground for algae.

Water district officials say they hope the agencies — now holding the cold water in Shasta to benefit salmon in the Sacramento River — will release it soon to help refill San Luis Reservoir. That would head off any shortages later this year that could require tougher conservation rules or heavy pumping from local groundwater aquifers, said Cindy Kao, the district’s imported water manager.

“If San Luis can start filling within a few weeks, we don’t anticipate there would be a need to increase conservation,” Kao said. “We are still sorting it out, but we don’t think there’s an emergency.”

Paul Rogers covers resources and environmental issues. Contact him at 408-920-5045. Follow him at Twitter.com/PaulRogersSJMN.