We did not encounter a thermocline. Maximum depth is 35 feet. Gary cruises through the gloom. There are few natural coves or other features that keep motorboats off your head. Much of the lake is shallow, and unreachable except by boat.
Visibility tends to improve later in the year, but is never great.
Echo State Park, on the east side of the lake, has camping, picnic areas, and boat launching. It is the ONLY shore access to Echo, unless you want to bike your scuba gear up the trail. Nearest dive services are in Ogden or Salt Lake City. In early or late season, you'll need to add a hood and gloves. In the shallows, fine moss covers some rocks.