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Almaden Lake Improvement Project

About This Project

The Almaden Lake Improvement Project reflects the water district’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. The loss of the integrity of Alamitos Creek has been detrimental to the health of the native fish population in the creek system. Further, having the Alamitos Creek flow directly into the lake allows for a direct deposition of naturally occurring mercury-laden sediment into the lake. This has resulted in 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.

Returning the natural creek features at this site will improve fish passage to the upper watershed, transport of sediment in the creek system, and return the riparian habitat to improve the wildlife corridor.

A separated lake will remain at the park. Imported water will be used as the water source for the separated lake.

Where are we now? 

Planning for the project began in 2012, with the 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.

Two of the proposed designs - Options 6 and 7 - received the most support, though they shared many similarities. Both kept a lake body on the east side of the restored creek section.

The district is preparing a draft Environmental Impact Report that evaluates both options and their impact on the surrounding area. The district further engineered Option 6 to the 30 percent level of design and it is the recommended alternative. This option best supports the project objective of minimizing park impacts. Option 7 proposed cutting into the parkland area where the boathouse currently sits. Option 6 does not cut into that area.


Almaden Lake Project artist rendering
San Jose
Start: 2012 / Finish: 2022
$4.2 million for planning and design through the Safe, Clean Water Program / $25 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

The district recently identified a water source for the lake as part of the project’s design: Imported water from the Almaden Valley Pipeline. The imported water contains less mercury than what comes from Alamitos Creek that is directly linked to the old New Almaden Quicksilver Mine located in the upper Guadalupe Watershed.

The project is currently in the design phase and a draft Environmental Impact Report (EIR) that will evaluate the project’s potential environmental impacts is under preparation. An EIR is required under the California Environmental Quality Act (CEQA) process. In early 2019, the report is expected to go to the district’s board of directors for certification. Construction could begin in summer 2021 pending the board’s approval, funding availability and permit acquisition and take about two years.


For More Information

Artist rendering of proposed design (click to enlarge)


Almaden Lake at several points in time (click to enlarge)
Environmental & Community Benefits

 Key Performance Indicators

  1. Complete planning and design for 2 creek/lake separations.
  2. 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.