two important subclasses of lakes are ponds, which typically are small lakes that intergrade with wetlands, and water reservoirs. over long periods of time, lakes, or bays within them, may gradually become enriched by nutrients and slowly fill in with organic sediments, a process called succession. when humans use the watershed, the volumes of sediment entering the lake can accelerate this process. the addition of sediments and nutrients to a lake is known as eutrophication.