You may have noticed over the summer months that the waters of the main body of Hayden Lake appeared clearer than normal. Lake clarity measurements completed during the summer 2023 document the high clarity, at times reaching 8.5 meters of visibility. Chlorophyll a measurement, a surrogate for the amount of algae present were correspondingly low. Actual algal counts from samples still being processed will likely support the chlorophyll a results. These conditions were created by lower total phosphorous in the lake than has ever been observed, an average of 3.7 micrograms per liter. This value is over a half microgram per liter below the previous four-year average of 4.3 micrograms per liter. These results reflect exceptionally good water quality in the main pool of the lake. The data collected this year and in the past three years indicate that the high-water quality of the main pool is reflected in the major bays around the main body, Mokins, O’Rourke, Windy and Berven. Unfortunately, this high-water quality would not be expected that the shallow northern arm of the lake (North of Henry’s Point). The shallow nature of most of the North Arm adversely affects its water quality.
There are both short term and long-term explanations for the general and recent decline in the total phosphorous concentrations of the lake. This year’s snowpack and resulting spring runoff were modest. Water yield to the lake was insufficient to spill water over the dike. The late spring, early and midsummer rains were of insufficient intensity to create significant runoff to the lake. These conditions did not allow replenishment of phosphorous to the lake, as existing upper water column phosphorous sank down with senescent algae and out of the lake’s photic zone.
Over the long term, total phosphorus has declined significantly. Total phosphorous concentration measured between 1975 and 2006 averaged 7.5 micrograms per liter. Over the past four years of measurement (2019-2022), the average is 4.3 micrograms per liter. The decline could be attributed to the fact that many of the phosphorous reducing projects prescribed in the Hayden Lake Management Plan Addendum have been completed. Projects, like removal of Mivoden’s sewage treatment from the lakeshore to a land application a mile from the lakeshore, fencing of livestock from tributary streams (Lancaster and Neilsen Creeks), decommissioning of forest haul roads in the Yellowbanks and Neilsen Creek (Deerfoot Ridge) watersheds, the paving of some roads (Mokins Bay Road), stabilization of roads including culvert replacements, and increased vigilance on lakeside and watershed development can be cited. In addition, the Forest Service has not significantly harvested timber in the watershed for over twenty-five years.
The current water quality trend may not hold because changes are afoot in the lake’s watershed. The Ridge Creek Fire which burned through most of August, burned over a quarter to a third to the lake’s largest watershed, Hayden Creek. The Forest Service’s initial assessment indicates most of the burn was light to moderate. However, the fire triggered a massive upgrade of road surfaces in the Hayden Creek watershed, with no attention paid to the locations that load sediment directly to Hayden Creek. Unless upgrades are made to address these sites, much of the aggregate placed on the road is destined to erode and be transported to Hayden Creek. Over the next few years, the fire and road improvements will likely result in more tons of sediment delivery to Hayden Creek, and that sediment will carry roughly 1.6 pounds of phosphorous per ton of sediment. The Forest Service will be laying out Honey-Badger timber sales starting next summer. These initial sales will be sold in 2025 and logged shortly thereafter. We can expect ten years of logging activity in that part of the Hayden Lake Watershed managed by the Forest Service. These sales will be required to meet the Federal Upper Columbia Fisheries Standards which are far more restrictive than Idaho’s Forest Practices Act Rules and Regulations. Maps provided during Honey-Badger’s environmental review indicated most timber sales would be near the ridgetops and well removed from streams. Like the impact of the Ridge Creek Fire, the effects will remain to be assessed how the Honey-Badger timber sales impact the plant growth nutrient (phosphorous) loading to Hayden Lake.

For a deeper dive into Hayden Lake water quality reporting, including the 2022 Hayden Lake TMDL Implementation Plan Update Report visit our Water Quality Monitoring page.