Stagnant water, algae, and poor filtration are all common causes of bad pond water odors. If you find your pond water smelling unpleasant, often like rotten eggs or sewage, there is likely a substance imbalance or build-up of waste causing the problem.

What causes a pond to smell?

Stagnant Water Without sufficient oxygen, aerobic bacteria can’t break up waste from animals and plants at the bottom of ponds, leaving the job to anaerobic bacteria. These organisms give off CO2 and hydrogen sulfide, which is the characteristic rotten egg smell.

Do fish ponds stink?

One of the most common causes of pond odor is not having your pond aerated. In the summer, ponds that aren’t aerated, stratify into different layers of water that have different temperatures. … ‘ The bacteria ultimately produces waste products, like carbon dioxide, the culprit of that rotten egg smell we all flee from.