Nitrogen from animal waste can be stored in bodies of water primarily as nitrates.
When animal waste enters water bodies, bacteria break down the organic nitrogen in the waste, leading to the production of ammonia, which can further be oxidized to nitrites and then to nitrates through a process called nitrification. Nitrates are often the most stable and prevalent form of nitrogen found in aquatic environments as a result of this process.
So, the correct answer is nitrates.