This indicator measures the amount of attached algae in the nearshore of Lake Tahoe. Attached algae or periphyton refers to a suite of organisms that grow attached to submerged surfaces (e.g. rocks, boats, buoys, piers). In Lake Tahoe, these include stalked diatoms, filamentous green algae, and cyanophytes. Excessive periphyton growth impacts the aesthetic qualities and impairs beneficial use of the shorezone. When periphyton dies off and breaks free each year, beaches can be fouled and water contact recreation affected. Regional programs such as stormwater reduction aim to reduce the amount of algae in the nearshore. Algae in the nearshore is monitored by UC Davis. 


Evaluation Map

Periphyton Monitoring Locations

2019 Evaluation

Insufficient Data to Determine Status or No Target Established
Little or No Change
View Evaluation

Applicable Standard

WQ6: Attain 1967-71 mean values for periphyton biomass in the littoral zone.

Key Points

  • There has been no significant change in periphyton in Tahoe since monitoring began 30 years ago.
  • A 2020 independent peer review of Tahoe’s periphyton monitoring confirmed that the program was technically sound. The reviewers hypothesized that stakeholder perceived increase in nearshore algal could be driven by metaphtyon (detached algae which are not captured in the existing monitoring program).
  • Agencies and the Tahoe Science Advisory Council are reviewing nearshore algal monitoring and assessing opportunities to modify the program to include all nearshore algae.
  • UC Davis has monitored periphyton in Lake Tahoe since 2000. Monitoring also occurred between 1982 and 1985 and 1989 to 1993. The primary periphyton monitoring work is regular sampling work referred to as “routine” sampling at nine sites annually (the number of locations has varied historically from six to ten). At each location algal biomass (as chlorophyll a) is sampled five times annually from natural rock surfaces at a depth of 0.5 meters below the water level at the time of sampling. A second type of sampling, referred to as “synoptic” monitoring occurs once a year at 40 additional sites. The timing of synoptic monitoring varies annually and is intended to capture biomass at its peak in the spring. The synoptic monitoring includes the collection of chlorophyll a at a sub-set of the sites, as well as a rapid assessment method that quantifies a periphyton biomass index (PBI).