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Almaden Lake Improvement Project

About This Project

The Almaden Lake Improvement Project reflects Valley Water's commitment to protect the environment, restore habitat and improve water quality. The project will restore the creek channel section within Almaden Lake Park and eliminate the current condition whereby Alamitos Creek flows through the lake. Having Alamitos Creek flow through Almaden Lake is unfavorable for the native fish population in the Guadalupe Watershed and further allows for a direct deposition of naturally occurring mercury-laden sediment into the lake. This has resulted in native fish (steelhead) potentially losing their way in the lake and falling prey to non-native fish (bass), as well as the lake having mercury-related water quality issues.

To address both the fisheries and mercury issues, the project will separate the creek from the lake by constructing a new levee in a north-south direction through the lake. The new levee will become the lake’s new west bank boundary and isolate the lake to the east side of the park. The new levee will also serve as the restored creek’s east embankment. Restoring the creek channel section means Alamitos Creek can flow directly into the Guadalupe River as it once did prior to the formation of the park in the 1980s. The accompanying image shows the proposed project. 

Natural creek features, such as riffles, pools, and runs, will be returned to improve passage for native fish to the upper watershed. Riparian habitat will also be returned to improve the wildlife corridor with its numerous ancillary benefits to a creek system. A separated lake will remain at the park along with its existing island and a new island. Water for the lake will be from an imported water source. To improve water circulation in the lake, the lake bottom will be re-contoured and water from the lake will be pumped to Valley Water's Alamitos Percolation Pond located near Valley Water's headquarter building.

Planning for the project began in 2012, with Valley Water conducting extensive hands-on outreach through 2015 to the community, holding public meetings and providing presentations to neighborhood associations, service organizations and the city of San Jose to educate all and garner input on the project's design. 


Almaden Lake
San Jose
Start: Summer 2023
$9 million for planning and design through the Safe, Clean Water Program / $50 million for construction
News and UpdatesNews and Updates
Reports and DocumentsReports and Documents
Environmental and Community BenefitsEnvironmental and Community Benefits
History and BackgroundHistory and Background
News & Updates

Algae blooms at Almaden Lake

Recreational park users may have noticed Almaden Lake's greenish color, and at times, it may have an odor. Algae commonly blooms in the summer months due to warmer temperatures and the stagnant water throughout the lake.

To better understand the conditions there, water quality specialists measured two different algae indicator levels in the lake in early August 2021 and determined that green algae levels near the lake's surface were relatively low. However, blue-green algae levels were high enough to suggest there is a larger bloom potentially forming.

The extreme drought has contributed to poorer lake conditions than in the past. The size of the blue-green algae bloom in Almaden Lake is due to the minimal flow in and out of the lake and high surface water temperatures. On Aug. 11, 2021, the lake's surface water temperature was 2.52F  higher than has ever been measured at the lake. Staff also observed no surface inflow to the lake from Alamitos Creek, which is due to the drought. 

Valley Water is coordinating with the City of San Jose, who owns the park around the lake and is responsible for posting signs around the lake should it need to be closed to access by park users. Valley Water will provide updates on the lake's condition as information comes in via Nextdoor and on this project page.   

Environmental Impact Report 

On May 11, 2021, Valley Water's Board of Directors certified the final Environmental Impact Report. 

To read the report, click the links below.

Final Environmental Impact Report

Appendices _ Final Environmental Impact Report

Notice of Determination

Missed our public meeting?

Valley Water hosted a public meeting on Jan. 8, 2020, to present the draft Environmental Impact Report (EIR). If you were unable to attend, you can still view the meeting on our YouTube channel by clicking here

For More Information

Environmental & Community Benefits

 Key Performance Indicator

  1. Construct 1 creek/lake separation project in partnership with local agencies.


  • Improves fish passage to spawning and rearing habitat within the Guadalupe Watershed
  • Improves steelhead trout habitat in the restored creek
  • Reduces mercury in Almaden Lake

Geographic Area of Benefit

  • San Jose
History & Background

Mining during California’s gold rush era played a role in the proliferation of mercury in local waters. Between 1850 and 1970, there was a release of about 6,500 tons of mercury from the New Almaden Quicksilver Mines into local creeks and rivers in the upper Guadalupe Watershed, about five miles from the project site.

The on-and-off stream gravel quarry operations along the east side of Alamitos Creek comprised of three main large pits around the 1960s created Almaden Lake. After gravel quarry operations ceased, heavy storm events eroded the levee that separated the creek from the quarry, resulting in discharge of creek waters into the former quarry area, creating the lake. The lake’s bottom is unnaturally varied due to the remnant pits. Remnant dikes that separated individual pits during quarry operations remain, but are now submerged below the water surface. In fact, the existing island in the lake is really a remnant dike.

Since its formation, mercury-laden sediment from the mines has deposited into the lake and accumulated at its bottom. The lake also suffers from high nutrient and organic matter loadings from algal blooms and waterfowl. The lake does not percolate and because of the remnant pits, it does not circulate well. This condition contributes to the bottom waters seasonally experiencing low oxygen or anoxic conditions. In those conditions, certain microbes transform mercury into methylmercury, a strong neurotoxin that accumulates in the tissues of organisms, such as fish in Almaden Lake.

The San Francisco Bay Regional Water Quality Control Board has adopted specific water quality objectives contained in its 2008 Basin Amendment Plan. Mercury conditions in Almaden Lake currently exceed these objectives and the proposed project looks to address methylmercury production in the lake to meet these objectives.  

Planning for the project began in 2012, with the water district conducting extensive hands-on outreach over two years to the community, holding public meetings and providing presentations to neighborhood associations, service organizations and the City of San José to garner input on the project’s design. Planning was deemed complete with the selection of project options #6 and #7.