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Tuesday, June 9, 2020

Record Secchi Readings on Big and Little Spirit Lakes

The first June sample event brought record water clarity (Secchi) readings for Little and Big Spirit Lakes since CLAMP began in 1999!

The Bahneys recorded an all time CLAMP record of 5.85 meters (19.2 ft) on Big Spirit (above), deeper than the 17 foot average depth of the lake. On Little Spirit Steve Franker could see all the way to the bottom of the lake at Site 2 (below). Note how the Secchi readings are underscored on his data sheet. This means the disk was sitting on the bottom. You might also have guessed it was sitting at the bottom because the lowered, raised and average readings are all the same but this can happen even when the Secchi disk is not sitting on the bottom -  hence the importance of underscoring when it does.

Why? Even though clarity readings are typically high in early summer before water temps and biological productivity have heated up, this is extraordinary. In the case of Big Spirit this may be due to the recent colonization of zebra mussels in the lake. First documented in Big Spirit in 2017, zebra mussels are filter feeders and can increase water clarity by several meters. It is unknown if zebra mussels have colonized Little Spirit. Stay tuned for more data in coming months!