It is important to pick up waste from your pet because 1. nutrients in the waste can increase the algae population 2. bacteria in the waste can infect aquatic organisms 3. mercury in the waste can cause mercury poisoning in fish 4. bacteria in waste decreases the amount of oxygen in water

4. Bacteria in waste decreases the amount of oxygen in water

Explanation:

Hello,

As long as the wastes have bacteria and they could affect aquatic organism, this is done because they decreases the amount of oxygen in water due to the fact that aerobic bacteria use oxygen like us to produce the required energy to live and to perform their metabolic processes as well.

Best regards.