Ask Lyn: What’s Happening Under the Surface in the Spring?

Dear Lyn,

Especially in Indiana our lakes experience a lot of extreme weather changes; winter ice to spring floods to summer heat. My question is, we see tulips and birds as the first signs of spring, but what happens in my lake in the spring?

Thanks,
Spring Fever

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Dear Spring Fever,

That’s a great question! Like humans and other animals, our lakes slow down and take a break during the winter. But in the spring they come back to life full force!

This year we have had high water from heavy rains and cooler temperatures, which makes for an interesting combination. Aquatic plants are just now starting to grow, and what we call “spring turnover” when the lake water mixes from top to bottom is taking place.

The influx of nutrients from the bottom water (hypolimnion), along with the excess nutrients and debris swept into the lake earlier this spring  will likely bring some bright green spring algae blooms.

What makes algae grow? Algae grow when there is adequate sunlight, enough nutrients (especially phosphorus), and the right temperatures for their particular needs – which makes blooms in the spring especially likely.

The amount of algae tends to be high in spring and early summer because of increasing water temperature, more sunlight, abundant nutrients from spring runoff, and low amounts of grazing by zooplankton (microscopic floating animals which eat algae). Because of their rapid growth, diatoms are often the algae that proliferate in the spring. In early summer, green algae usually dominate. Late summer and fall may be dominated by blue-green algae which can produce dangerous algal toxins. To Learn more about algae, check out this great information sheet from Washington!

Happy Spring!