The Lamar River in 2022: Record Flood, Then a Hot, Dry Summer

This report covers monitoring of the Lamar River in 2022.

The Park Service's Greater Yellowstone Inventory and Monitoring Network checks the water quality of the Lamar River and analyzes its flow every year. The river's water is of high quality; about three quarters of its watershed lies inside Yellowstone National Park.

Figure 2. An overview of the Lamar River sampling location (denoted by the yellow star) relative to the river's confluence with the Yellowstone River (the Yellowstone River can be seen on the left side of the image). NPS.

The Lamar River. National Park Service.

The river

The Lamar drains 668 square miles (1,730 km²) and is the largest tributary of the Yellowstone River inside the park. It is named for Lucius Quintus Cincinnatus Lamar, secretary of the interior under President Grover Cleveland from 1885 to 1888. It rises in the Absaroka-Beartooth Mountains and runs nearly 44 miles (70 km) to join the Yellowstone near Tower Junction, picking up Cache Creek near its headwaters and Soda Butte and Slough creeks closer to its mouth. Most of its watershed is federal land, and 73% of it, 1,270 of 1,730 km², lies within the park. The network samples the river just above its confluence with the Yellowstone.

Lamar River sampling location. NPS.

Figure 1. The boundary of the Upper and Lower Lamar River watersheds includes the Lamar River's major tributaries. Almost three-quarters of the watershed is within Yellowstone National Park. Sampling occurs above the confluence of the Yellowstone River. NPS.

Flow

The U.S. Geological Survey runs the river's only stream gage (USGS 06188000), just above the confluence, in cooperation with the park. It has daily flow records back to 1923, with a gap from fall 1969 to summer 1988.

The Lamar has a typical snow-driven flow pattern: its peak flows can run two orders of magnitude, about 100 times, higher than its base flow. From 1924 to 2021, annual peaks averaged 8,059 cubic feet per second (cfs), on June 4 on average, and the lowest daily flow of each year averaged 70 cfs.

In June 2022 the Yellowstone River and its tributaries, the Lamar among them, had a 500-year flood. Until late May the Lamar ran at or below its long-term average. By mid-June, heavy rain and warmer nights sped the melting of snow onto already soaked ground, and on June 13, the first day of the flood, the river peaked at a record 23,800 cfs. The previous record, set in 1995, was 15,600 cfs.

Average daily discharge of the Lamar River near Tower Ranger Station, 2022 compared with 1924–2021, with the 25th and 75th percentiles. National Park Service.

Despite the record flood, flows were back to the long-term average by early July and below it by mid-July, because of a warm, dry summer. July brought 50% less precipitation than the 1991–2020 average, and air temperatures at Tower Falls ran 3°C above average. The year's lowest flow was 76 cfs.

Water quality

Suspended sediment and total phosphorus normally peak during high flows, while sulfate, calcium, sodium and similar constituents are lowest then and rise as the river drops toward base flow. Nitrate plus nitrite and ammonia have usually been below detection.

A 1-m wading rod is attached to a DH-81 hand-held sampler to collect water samples across the Lamar River. NPS.

The network sampled the river seven times between March and October 2022, testing water chemistry along with temperature, specific conductance, dissolved oxygen, pH and turbidity. Results matched earlier years until the June 13 flood. Afterward:

• Phosphorus, normally from below detection to 0.07 mg/L, ranged from 0.04 to 0.14 mg/L.
• Nitrate plus nitrite, usually below detection, ranged up to 0.07 mg/L.
• Ammonia was mostly not detected.
• Total suspended solids were high, from 2 to 76 mg/L. They usually peak in mid to late summer as the river returns to base flow.

The flood knocked out the gage's temperature sensor from June 13 to August 15, 2022. Water was warmest in summer, at base flow. In mid-August daily temperatures ran 2 to 3°C above average, and on August 17 the river passed the Wyoming Department of Environmental Quality's 20°C (68°F) maximum for cold-water fisheries, the only day it did.

Daily maximum water temperature in the Lamar River in 2022 and 2017–2021. The dotted line is Wyoming's maximum temperature guidance for cold-water fish. National Park Service.

How the river is sampled

The network samples monthly while the river is free of ice, following the USGS National Field Manual. Staff wade across the river with a one-liter DH-81 sampler on a one-meter rod, collecting water from top to bottom at several points across the channel, then mix it in an eight-liter churn splitter and fill bottles that go overnight to an EPA-certified laboratory. A handheld multiparameter sonde measures temperature, specific conductance, dissolved oxygen, pH and turbidity at four points across the river.

A handheld, multi-parameter instrument is used to collect water quality parameters: temperature, specific conductance, dissolved oxygen, pH, and turbidity. NPS.

Preparing water samples at the Lamar River. National Park Service.

Protected waters

Under the Clean Water Act, Yellowstone's surface waters are Outstanding National Resource Waters. They are also designated Outstanding Resource Waters in Montana and Class 1 Outstanding Natural Resource Waters in Wyoming, meaning high-quality waters that support fish or supply drinking water, where no further degradation from point-source discharges other than dams is allowed. The Lamar's results are compared with EPA's national recommended criteria and Wyoming's surface water quality standards.

Sources

• National Park Service, Greater Yellowstone Inventory and Monitoring Network, "Water Resources Monitoring in the Lamar River near Tower Ranger Station, Wyoming, 2022" (2024). https://www.nps.gov/articles/000/lamar-river-monitoring-2022.htm
• Monitoring data: NPS DataStore, https://irma.nps.gov/DataStore/Reference/Profile/2302791, and the Water Quality Portal (site 11NPSWRD_WQX-YELL_LM000.5M), https://www.waterqualitydata.us/
• Flow and temperature: USGS National Water Information System, station 06188000, https://waterdata.usgs.gov/nwis/uv Pictures an earlier version of this page left out were restored on 2026-09-26.