Complex sentence: The lake is very shallow, about three feet (1 m) deep throughout most the lake, but there is one deep spot, about 54.5 feet (16 m) deep, due to dredging for sand in years past.
Split into simpler sentences: The lake is very shallow, about three feet (1 m) deep throughout most the lake. There is however one deep spot, about 54.5 feet (16 m) deep, due to dredging for sand in years past.