Arrange the following events in sequence.

(a) Excessive growth of planktonic algae

(b) Deposition of nitrates and phosphates

(c) Deprivation of dissolved oxygen

(d) Death of aquatic organisms

The prime contaminants are nitrates and phosphates, which act as plant nutrients. They overstimulate the growth of algae, causing unsightly scum and unpleasant odours, and robbing the water of dissolved oxygen vital to other aquatic life. At the same time, other pollutants flowing into a lake may poison whole populations of fish, whose decomposing remains further deplete the water’s dissolved oxygen content.