NRAP Focus Area
Focus Area - Public Health
Basics
Focus Area - Public Health
Human interactions with nearshore waters are primarily associated with
recreational activities and with consumption of treated and untreated waters drawn from the lake. The characteristics and quality of water used for consumption are regulated under separate state and U.S. EPA provisions. Existing state and local programs for tracking presence of harmful micro-organisms and toxic compounds serve as nearshore human health indicators.

Ultra-oligotrophic lakes do not generally have issues with toxicity or harmful microorganisms, unless there are discharges of sewage or waste. Sewage and industrial discharges are not allowed into Lake Tahoe, although surface stormwater runoff to the lake from urban areas and some recreational activities could conceivably contribute toxic chemicals or pathogens.
NRAP Focus Area Key Photo
Camp Richardson Beach, South Lake Tahoe
State of Knowledge

The primary public health concerns associated with Lake Tahoe's nearshore are (1) harmful algal blooms; and (2) fecal indicator bacteria concentrations, which indicate the possible presence of pathogens and viruses which can make people sick.

The first known harmful algal bloom (HAB) occurred in the Lake Tahoe Keys in August 2017. The level of measured cyanotoxins was below any health concern, but the area was posted to warn the public of the potential danger and to protect pets. The Lahontan Water Board monitors the California side of Lake Tahoe Basin for HAB issues, and the Nevada Department of Environmental Protection (NDEP)  monitors the Nevada side. Both agencies respond to reports of possible HABs around the Lake Tahoe Basin and post sampling results and other information as appropriate. More information about HAB sampling in California and Nevada can be found here: Lahontan Water Board's HAB program & NDEP HAB Program.

The most recent fecal indicator bacteria monitoring for Escherichia Coli (E. coli) was conducted in 2025 between June and September at eight recreational beaches around Lake Tahoe. The monitoring report containing the results of from the 2025 monitoring season will be available soon. In August 2025, the monitoring program identified Camp Richardson beach water quality as impacted by E. coli. Water Board staff initiated daily water quality sampling, and the concurrent source investigation identified a broken sewer lateral near the beach, which was fixed the same day it was found. Daily monitoring continued until E. coli water quality returned to normal levels, which took approximately two weeks. During this period and out of abundance of caution, the United State Forest Service (USFS), the landowner of the affected beach, posted caution signs warning water contact recreators of the potential risks posed by the water quality in the area. Camp Richardson beach water quality is now within expected E. coli ranges for Lake Tahoe, which are usually below 20 colonies per 100 milliliters (mL) of water. For reference, the California water quality objective for E. coli is 320 colonies per 100 mL in a single sample, or 100 colonies per 100 mL in a long term average of samples. More information about the E. coli water quality monitoring at Lake Tahoe can be accessed in this StoryMap.

Findings

Nearshore Human Health, E. coli monitoring

Approach

Water quality samples for E. coli are taken throughout the summer at popular beaches around Lake Tahoe. E. coli is an indicator of the presence of harmful pathogens or viruses associated with recent contamination by wastewater or other fecal contamination. Individuals who swim in or contact water with elevated levels of E. coli may be at risk of getting sick because of potential exposure to harmful pathogens or viruses associated with wastewater or other fecal contamination.

Harmful Algae Bloom (HAB) Monitoring

Approach

On the California side of the lake, water samples are collected and tested for the presence of HABs and their associated toxins at various locations. Water Board staff respond to new bloom reports, and also administer a pre-holiday assessment monitoring program at several California beaches. HAB monitoring associated with pre-holiday assessments is intended to collect information to inform the public in California about the safety of recreational beaches during high use holiday weekends including Memorial Day, Fourth of July, and Labor Day.