Sunlight glimmers on Lake Tahoe on a spring morning in April as the John LeConte, the 48-year-old research vessel for the UC Davis Tahoe Environmental Research Center, motors across the glassy water. The engine turns over with a rhythmic revving that eventually fades into a background hum. Gentle waves ripple out from the prow, but the water is otherwise completely still. I’m onboard the John LeConte with a group of scientists. We’re heading to the middle of Lake Tahoe to get a picture of what’s happening beneath the surface of the water, all the way down to the deepest parts of the lake.