Maximum depth is 244 m, with an average depth of 86 m. The main portion of the lake is a smooth east-west trough divided into three basins . Water depths descend gradually towards these basins. The eastern part of the lake is less than 50 m deep throughout, with a complex bottom relief . Upwelling occurs along the western edge of the lake and prevents stratification in this part of the lake.
Primary productivity is moderate, about half that of Lake Erie.
Water clarity is usually in the 5-10 m range, while the lake's retention time is about six years. These bluffs are generally 3-10 m in height, but are up to 100 m high in the area of the Scarborough Bluffs. Wind-blown shore sediment has created several barrier beaches , sand dunes and sand spits . Small wetlands occur locally. Some 85 fish species have been recorded in Lake Ontario.