Like the Bahama’s – Only colder: Diamond Lake, Cass, MI. The lake is 1,078 acres in size, 60% of the lake is less than 10 feet deep, and is 64 feet at its deepest. Shoal areas (less than 20 feet deep) account for about 68% of the surface area of the lake. The island in the middle is called Diamond Isle and is ~ 43 acres. General access to the island is via ponton boat. There is a rubble wreck of an 60 foot old steam boat called the “South Bend” off the northeast point of the island in ~40 feet of water.