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. 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. 


Nearshore Attached Algae.JPG
Summary statistics (# observations, mean, median, std. dev.) for periphyton biomass (Chlorophyll a mg / m2) and p-value for trend analysis for change in biomass. Trend analysis combine all routine sites to assess Lake-wide periphyton trends. Where analysis of trend indicated a significant trend, the direction of the trend is indicated. Observations where Lake Elevation >= 6225 ft or where the sampling depth has been submerged for less than 1000 days (< 1000 day) are thought to reflect trend in stalked diatoms and/or filamentous green algae. Observations where lake Lake Elevation <6225 ft or where the depth has been submerged for more than 1000 days (< 1000 day) are thought to be influenced by blue-green algae. Table adapted from (Hackley et al., 2016a).

Evaluation Map

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Map of Nearshore Attached Algae 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 algae could be driven by metaphtyon (detached algae which is not captured in the existing monitoring program).
  • No attainment call has ever been made for nearshore attached algae because the baseline against which the standard is to be assessed (1967-71 mean values for periphyton biomass) is not known.
  • 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.