Background
Lake Temescal
Lake Facts
LocationOakland, CA
Size9.6 acres
Age157 years old
Initial depth~70 ft
Depth (2024)16.7 ft
Average depth9.7 ft - polymictic
Problems Identified
- HABs since the 1970’s
- Eutrophic
- Sedimentation
- Aquatic Weeds
- Anoxia
- Internal / external loading
Pre-Treatment Conditions
Cyanobacteria Toxins (Microcystins) between 2023 and 2024
Pre-Treatment Conditions
Dissolved Oxygen between 2023 and 2024
Treatment Strategy
Plan for 2025
Treatment 1
Phosphorus remediation treatment
ACH and Phoslock
Treatment 2
OST installation
Installation of an Oxygen Saturation Technology System (OST) to mitigate low hypolimnetic oxygen conditions
Monitoring
Study design
4 locations with samples collected at 1m depth and 0.5m above the bottom, before, one week after, 1, 2, 3, and 6 months after
Pre-Treatment Analysis
Level 2 Fractionation Analysis of 4 sediment samples in April 2025
How was the dose of 3000 gal and 20,000 lbs. calculated? Why use both, ACH and Phoslock?
Pre-treatment Alkalinity
223 mg CaCO₃/L at 1m
264 mg CaCO₃/L at 0.5m above bottom
Eli to add dose calculation
Treatment Application
ACH / Phoslock application June 3rd & 4th
Treatment Application
OST was installed June 9th
Results
1. pH stayed within 1 pH unit of pre-treatment conditions
Results
2. Total Alkalinity, Aluminum and dissolved Aluminum
Before and After
Results
3. Reduced Microcystin toxins / No swim beach closures in 2025
Results
4. Reduction in Total Phosphorus
Results
4. Dissolved Oxygen between 2024 and now
Results
5. Chlorophyll
Chlorophyll (µg/L) Trophic class
0-2.6 Oligotrophic
2.6-7.3 Mesotrophic
7.3-56 Eutrophic
56-155+ Hypertrophic
Results
6. Absolute Phytoplankton Abundance
3,038
6,430
14,050
3,125 6,250
Conclusions
Summary
- OST creates the desired oxygen levels in Lake Temescal
- Swim beach stayed open through the swim season without HABs closures
- Phosphorus results are still low as of September
- Improved water quality and community composition
- 2025 summer was unseasonably cool - might have contributed to the success
- Plan for 2026: rinse and repeat - no guarantee to see the same outcome
Conclusions
Lessons learned
- ACH is a good alternative to ALUM with little impact on pH if applied evenly throughout the lake
- ACH / Phoslock and Oxygenation in combination seem effective to reduce Phosphorus and mitigate toxins
- Aquatic weeds love clear water - need for additional intervention
DO NOT WASTE RESOURCES ON SHORT-TERM FIXES
