Lake Sentinel is a lightweight solar-powered monitoring buoy that reads six water variables every 30 minutes and streams them straight into your lake's account. It weighs about eight pounds, drops in the water without a crane or a technician, and is typically deployed in under an hour by whoever is available.

The sensors work by fluorescence. Chlorophyll-a indicates algae generally; phycocyanin is specific to cyanobacteria, the blue-green algae that produce toxins. Reading both means you can tell a harmless green algae bloom from the one that closes a beach — and you can see it building while the water still looks fine.

Lake Sentinel is leased, not sold — the only item in the Toolbox on that basis. Lease periods are 1, 3, 6, and 12 months.