--- id: scenarios/lake-merritt-oakland about: label: 'Low oxygen in Lake Merritt, Oakland' description: >- A tidal lagoon in the middle of Oakland, opened wider to San Francisco Bay in 2013, still runs short of oxygen in late summer and winter, and a Bay algal bloom killed thousands of its fish in 2022. Which mix of tide gate operation, aeration and other measures keeps its fish alive? tags: - Lake Merritt - dissolved oxygen - algal blooms - tidal lagoon - fish kill - tide gates scenario: place: 'Lake Merritt and the Lake Merritt Channel, Oakland, California' since: '2022' scale: community domains: - water - ecology - people relations: - predicate: needs target: data-sources/inaturalist - predicate: needs target: engines/deltares-delft3d provenance: origin: agent sources: - title: Lake Merritt Water Quality (City of Oakland) url: >- https://www.oaklandca.gov/Government/Oakland-Improvement-Projects/Lake-Merritt-Water-Quality - title: Lake Merritt Water Quality Management Pilot Project (City of Oakland) url: >- https://www.oaklandca.gov/Government/Oakland-Improvement-Projects/Lake-Merritt-Water-Quality/Lake-Merritt-Water-Quality-Management-Pilot-Project - title: Lake Merritt Harmful Algae Bloom Updates (City of Oakland) url: >- https://www.oaklandca.gov/Government/Oakland-Improvement-Projects/Lake-Merritt-Water-Quality/Lake-Merritt-Harmful-Algae-Bloom-Updates - title: Lake Merritt Healthy Lake Initiative (City of Oakland) url: >- https://www.oaklandca.gov/Government/Oakland-Improvement-Projects/Lake-Merritt-Water-Quality/Lake-Merritt-Healthy-Lake-Initiative-1 - title: Clean Lake Initiative (City of Oakland) url: >- https://www.oaklandca.gov/Community/Community-Development/Sustainability-Environment/Creeks-Watershed-and-Stormwater/Clean-Lake-Initiative - title: >- Lake Merritt Advance Restoration Plan Project (San Francisco Bay Regional Water Quality Control Board) url: >- https://www.waterboards.ca.gov/sanfranciscobay/water_issues/programs/TMDLs/LakeMerrittAdvanceRestoration.html - title: >- Lake Merritt 2023–2025 Dissolved Oxygen Data Analysis, Final Staff Report (Water Board, October 2025) url: >- https://www.waterboards.ca.gov/sanfranciscobay/water_issues/programs/TMDLs/LakeMerritt/Lake%20Merritt%20DO%20Analysis_October_Final.pdf - title: >- Lake Merritt June 2025 Small-Scale Fish and Shrimp Mortality Events (Water Board, October 2025) url: >- https://www.waterboards.ca.gov/sanfranciscobay/water_issues/programs/TMDLs/LakeMerritt/June%202025%20Lake%20Merritt%20Aquatic%20Mortality%20Events%20Report_October_Final.pdf - title: >- Lake Merritt Low Dissolved Oxygen Advance Restoration Plan: 2024-2025 Nutrient Data Analysis (Water Board, January 2026) url: >- https://www.waterboards.ca.gov/sanfranciscobay/water_issues/programs/TMDLs/LakeMerritt/LM_Nutrient_Analysis_Report.pdf - title: About Lake Merritt (Lake Merritt Institute) url: 'https://lakemerrittinstitute.org/about-lake-merritt/' - title: >- City of Oakland moves forward with Lake Merritt Healthy Lake Initiative (Lake Merritt Institute, 11 August 2026) url: >- https://lakemerrittinstitute.org/2026/08/11/city-of-oakland-moves-forward-with-lake-merritt-healthy-lake-initiative/ - title: >- Measure DD Lake Merritt Improvements: Lake Merritt Boulevard & Park (project sheet) url: >- https://waterfrontaction.org/waterfrontaction/map/dd_updates/12th_update.pdf - title: >- Measure DD Lake Merritt Channel: 10th Street Lake Merritt Channel (project sheet) url: >- https://waterfrontaction.org/waterfrontaction/map/dd_updates/channel_update.pdf - title: 'Lake Merritt: The Revival of Oakland''s Jewel (SPUR, 22 January 2015)' url: 'https://www.spur.org/news/2015-01-22/lake-merritt-revival-oaklands-jewel' created: '2026-10-23' reviewed: '2026-10-23' reviewed_by: 'Claude, from the sources listed' status: draft --- Lake Merritt is a brackish tidal lagoon in central Oakland, 8 to 10 feet deep.[^10] The Lake Merritt Institute gives it 140 acres and the Water Board 150.[^6,10] A 4,650-acre urban watershed drains into it through more than 60 storm drains, and Bay water reaches it through the Lake Merritt Channel.[^5,9,10] Oakland's Measure DD bond, approved in 2002, paid in part for opening that channel.[^14] In July 2013 a dam and a twelve-lane road at 12th Street were replaced with bridges, a boulevard and a park, which SPUR reported raised the lake's tidal flow by 50 percent.[^12,14] A second Measure DD project, to replace the culverts under 10th Street with a bridge, was under way in 2015.[^13,14] Tide gates at the county's pump station near the channel mouth still control how much Bay water comes in, and are closed for flood control and other needs.[^8,9] In August 2022 a bloom of the alga *Heterosigma akashiwo* spread from the Bay into the lake.[^3,6] Oxygen fell to near zero across most of it for several days,[^6] and fish died in large numbers: the City says tens of thousands,[^3] and a later Water Board report puts the toll at up to 10,000 organisms.[^8] The lake is listed as impaired for low dissolved oxygen, and the Water Board is now writing a restoration plan for it.[^6] ## Who needs an answer - The City of Oakland, which has to choose which measures to install and where. It ran a pilot of aeration and oxygenation devices from 2023 and replaced the one that did not work with a diffused aeration system in January 2026.[^2,11] It has $959,757 in federal money for a Healthy Lake Initiative running to 2029.[^4,11] - The San Francisco Bay Regional Water Quality Control Board, whose Advance Restoration Plan will recommend actions for a City lake management plan.[^6] - The Alameda County Flood Control and Water Conservation District, which operates the tide gates[^9] and has to weigh flood protection against flushing. - Rowers and sailors, and the volunteers of the Lake Merritt Institute and the Rotary Nature Center Friends, who reported the two small die-offs of June 2025.[^6,8] ## The domains it chains Tides and gate operation in the channel.[^9] Rain and storm drains, which can lay fresh water over the salt.[^5,7] Nutrients, more than 99% of which the Water Board estimates come in from the Bay, and the algae they feed.[^9] Oxygen at the surface and on the bottom, which differ most in the narrow Glen Echo arm, while both arms fall short of oxygen more often than the center.[^7] Shrimp, gobies and larger fish, and the people who row, sail and walk around the lake every day. ## What a twin should let people try - Gates: how long a closure can last in summer or winter before the bottom water of the arms runs out of oxygen. The first June 2025 die-off came two days after the gates reopened from an eleven-day closure, the second after a shorter closure of about a day. The Water Board could not tie them to gate operation and plans a fuller analysis of past closures.[^8] - Flushing against feeding: more Bay water mixes and oxygenates the lake but also brings in the nitrogen that limits algae there.[^9] What does more or less exchange do to both? - Aeration: where fountains or diffusers would do the most, given that the oxygenation device in the Glen Echo arm did not perform as expected.[^2] - The next Bay bloom: how fast a red tide like 2022's would empty the lake of oxygen, and whether early gate closure or aeration would buy time. ## Where to start The City and the Lake Merritt Institute have run three continuous monitoring stations since 2023, measuring oxygen, temperature and salinity at surface and bottom.[^7] Their readings are published through the City's LakeTech dashboard.[^6] The Water Board ran two more from June to October 2024 and posts its nutrient data as a spreadsheet beside its reports.[^6,7,9] Dead fish have been logged on [iNaturalist](/data-sources/inaturalist/), where the California Department of Fish and Wildlife set up an SF Bay Harmful Algae Bloom 2023 project for such reports.[^3] A coastal flow and water-quality model such as [Delft3D](/engines/deltares-delft3d/) could take the channel, the gates and the lake together.