Complex sentence: Lake Whatcom was placed on the Environmental Protection Agency's 303 (d) list for impaired water bodies in 1998, due to low dissolved oxygen (DO) levels, which are directly related to the amount of phosphorus Lake Whatcom receives.
Split into simpler sentences: Lake Whatcom was placed on the Environmental Protection Agency's 303 (d) list for impaired water bodies in 1998, due to low dissolved oxygen (DO) levels. Low Dissolved oxygen are directly related to the amount of phosphorus Lake Whatcom receives.