Thick mats of rooted and semi-buoyant aquatic vegetation, mostly native potamogeton, growing along the shoreline near Rancho McCrea, upstream of Lakeside Lodge. Mixed in with the vegetation along the surface is harmless filamentous algae.
Why are there so many plants growing in Island Park Reservoir this year? Wind, y'all. The answer is wind.
Windy conditions in May + June kept Island Park Reservoir well-mixed, keeping dissolved oxygen levels high from the water surface on down to the reservoir bottom. High dissolved oxygen at the bottom of the reservoir promoted growth of rooted plants ("macrophytes"). These plants generate oxygen and keep dissolved oxygen + water clarity high. Good water clarity means more sunlight to fuel more plant growth.
Is this similar to a lake "turning over'?
Yes! The wind was so powerful it mixed the warm surface layer with the cold bottom layer. Those layers usually stay separate in the summer so this is highly unusual, maybe even unprecedented.
We are witnessing the highest plant growth rate in our 10 years of monitoring and there's still much more to learn. These conditions aren't great for reservoir boating or downstream aesthetics, but they are more favorable to the ecosystem than harmful algal blooms.
Addressing water quality concerns related to Island Park Reservoir are part of HFF's DIRTT Plan. With enough funding and community support, we may be able to manually mix or aerate the reservoir with manmade infrastructure to improve water quality in the reservoir.
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