Watching clarity emerge from its drivers, as the readings come in.
The latest readings from the Tahoe Environmental Observatory Network — lake sondes sampling water quality every fifteen minutes, and forest stations tracking the soil, air and trees of the watersheds that feed the lake. Each station saves up its readings and sends them in twice a day, so the newest numbers here are usually a few hours old.
What’s new
Three anchors on the lake
The three telemetered sondes, measuring the lake itself every fifteen minutes and sending those readings in twice a day. Each card shows the latest reading and its last two days.
Why oxygen appears three ways
Oxygen appears three ways on purpose. DO is the concentration. DO sat is TEON's published saturation percentage, which is referenced to a sea-level atmosphere. DO sat (local) is the same water measured against air pressure at the lake surface — 1,898 m, about 79.5 % of sea level. The difference is not cosmetic: 81 % reads as oxygen-stressed water, while 102 % of what the water can actually hold there means photosynthesis is running ahead of respiration. Derived from TEON's own concentration and temperature, so it depends on their measurements rather than their saturation assumption.
Hand-collected sondes
Two of the five lake sondes are self-logging: they store to internal memory and are read by boat and snorkel, roughly monthly. Their records are the most complete in the network — 98.8 % against 73.6–96.8 % for the telemetered ones, because there is no radio link to drop packets. What they are not is current. These cards show the period of record we hold rather than a live reading, and what the next collection would extend from.
The network
Every instrument in the basin with a coordinate — TEON's lake sondes, forest loggers, stream gauge and cameras, plus the USGS creek gauges. One marker per physical location rather than per endpoint, because a single forest tripod reports under three or four different sensor names. The dashed line is the transect: two stations 64 metres apart in latitude on opposite shores.
Shade the 60 stream catchments by any of the climate and landscape variables below. Annual precipitation is the one to start with: it runs from about 1,460 mm on the northwest shore down to 480 mm on the east, and that threefold gradient is the rain shadow the transect exists to measure.
Forest stations
Each station is a Campbell logger reading soil moisture and temperature at two depths, air temperature and humidity, and at five of them a set of band dendrometers measuring stem diameter — which both grows through the season and swells and shrinks daily with the tree's water content.
The trees, working for water
A band dendrometer is a fine metal band around a trunk, read to the micrometre. A stem refills with water overnight and shrinks through the day as the tree loses water through its needles faster than its roots can replace it. How far it shrinks between the morning peak and the afternoon low is how hard the tree worked for water that day: the more, the drier the air or the soil.
Same weather, two watersheds
Homewood and Glenbrook 5 sit 64 metres apart in latitude on opposite shores of the lake — the same line across the map, one side facing the Pacific storms and one side in the Sierra rain shadow. Both are upland hillslope stations, and both readings below are taken at the same instant, because air temperature and humidity swing far too much across a day for "latest at each site" to mean anything.
Field cameras
Five stations carry cameras logging into TEON's LoggerNet bucket.
The lake and its outlet
Lake Tahoe's surface elevation, and the single channel every drop leaving it passes through. Daily mean outflow at the outlet has been measured since 1895 — 131 years, a baseline no new sensor network can manufacture.
Tributaries
USGS gauges on the creeks feeding the lake, monitored for discharge, sediment and water quality since the late 1980s. Five carry real-time turbidity — the same measure as TEON's in-lake sondes, from independent instruments, which makes them the cross-check on readings like Sunnyside's faulty turbidity channel.
Beyond TEON
Context from outside the network, kept apart from TEON's own readings. None of it feeds TEON's numbers above. On the map, these stations sit beneath TEON's pins and can be switched off in the layer list.
How clear the lake is, measured by hand UC Davis TERC's Secchi disk record, since 1967
The measurement this site is named for. Since July 1967, UC Davis's Tahoe Environmental Research Center has lowered a white disk from a boat and recorded the depth at which it disappears, about every two weeks at an index station off the west shore and, since 1980, at a second station mid-lake. TEON's sondes measure what clouds the water; this is how far you can actually see into it.
Where the rain fell Precipitation from three SNOTEL gauges, beside the transect's soil
The soil tells you a storm arrived; it doesn't say how much fell. For that, secchi reads three stations of SNOTEL, the federal snow-survey network: Ward Creek #3 and Rubicon #2 on the west shore, Marlette Lake on the east. Each bar is a month of precipitation, rain and snow together, with the west shore above the line and the east below it.
The Snow Lab at Donner Summit UC Berkeley's snowpack record, since 1879
UC Berkeley's Central Sierra Snow Laboratory sits at 2,100 m on the crest about 30 km northwest of Homewood, outside the basin and on its wet side. It is context for the season, not one of the transect's shores: it typically gets far more snow than anywhere around the lake.
Weather at the airports South Lake Tahoe and Truckee, the National Weather Service's daily record
The only weather records here taken at lake level. South Lake Tahoe's airport is in the basin, about 5 km from the south shore; Truckee's is just outside it, in Martis Valley, and also measures snowfall.
Wildfire smoke. NOAA's satellite smoke analysis put smoke over the lake on 114 days since June 2024, mostly light. In 2025 and 2026, the summers the lake sondes were running, it left no mark that can be told from chance in their chlorophyll, blue-green algae, turbidity, oxygen or temperature.
Observatory inventory
TEON launched publicly on Sept 15, 2026 and is still building out. Below is every sensor in the current inventory. Green dots are reporting within the last day; amber have been quiet longer; grey have been dormant a while — often seasonal, since many lake sondes get pulled over the summer for maintenance.
Download the data
Pick a dataset, the stations and variables you want and a period, and
download just those readings as a CSV. Whole datasets are below too:
Parquet for Python, R and DuckDB, and gzipped CSV by year for Excel.
Values are exactly as stored. A
quality_flag column marks readings that look wrong, such as
impossible values, scrambled sonde channels, duplicated records and
sensors reading below zero.