F24 Kootenay Lake Nutrient Restoration Program – North Arm

This ongoing restoration program addresses nutrient losses in Kootenay Lake resulting from the construction of Duncan Dam.

In this bottom-up approach, the addition of nutrients—nitrogen and phosphorus in the form of liquid agricultural-grade fertilizer—from April to September support phytoplankton populations that are suitable for the production of daphnia, a main food source for kokanee.

This project also includes the coordination and technical and operational oversight of monitoring several trophic levels, as well as data analysis and reporting.

Update: Nutrients added to Kootenay Lake

Between April and September 2023, this project added nutrients to the North Arm of Kootenay Lake to improve the food web impacted by reservoir creation. Field work monitored the effects of nutrient additions on the food web.

Monitoring showed that kokanee spawner escapement—at nearly 154,000—was still low from a historical perspective, but the highest since 2013.

There has been an increase of in-lake survival of kokanee, resulting in a substantial improvement in kokanee biomass, again the highest since 2013.

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Final report: executive summary

Nutrient additions occurred only in the in the North Arm of Kootenay Lake in 2023. In the North Arm a total of 39.5 MT of phosphorus and 206 MT of nitrogen were added in the form of liquid agricultural grade fertilizers between May 5th and September 8th, 2023. Nutrient additions in the South Arm did not occur in 2023.

Total dissolved phosphorus means in 2023 were 2.5 μg/L in the North Arm and 2.2 μg/L in the South Arm, similar to previous years and indicative of an oligotrophic system. Dissolved inorganic nitrogen was again high in 2023, a pattern observed in both the North and South Arms of Kootenay since the early 2010s. The zooplankton cladoceran species Daphnia in 2023 was above the pre-Kokanee collapse mean, however was below the collapse era mean. Copepods (the zooplankton prey when Daphnia are not present) were below average in both the North and South Arms. Mysid densities in Kootenay lake were above average again in 2023, largely driven by higher abundances of immature individuals later in the season.

There were 153,673 kokanee spawners enumerated for the North Arm of Kootenay Lake in the fall of 2022. Kokanee fry (age 0) abundance was 10 million and the age 1-3 abundance was 2.1 million fish. Survival from age 0-1 increased to 18% and survival from 1-2+ was among the highest on record at 82%. The improvement in in-lake survival resulted in a substantial improvement in Kokanee biomass to 7.0 kg/ha, the highest since 2011.

There was a decrease in bull trout enumerated on Kootenay Lake, through redd count surveys. In 2023, the total count for index systems (Meadow, Kaslo/Keen, Midge, Crawford, and Coffee Creeks) was 244 redds. However, predator removal actions on Kaslo (a fisheries management action to support Kokanee recovery) resulted in the removal of 384 bull trout prior to spawning. Had removals not occurred, the total estimate for Kootenay Lake index tributary redds would have been in the vicinity of 436 in 2023.