Ammonia is deadly. It is primarily created through the fish’s gills, kidneys and intestinal waste. Decaying uneaten food, plant material and leaves also contribute to ammonia accumulations. Ammonia is reportedly the leading cause of fish stress, breaking down his immunity system and leading to bacterial disease. Measurable to high levels of ammonia is common in new ponds (and aquariums), over-stocked ponds and established ponds from heavy feeding in the spring prior to biological bacteria growth or from inadequate filtration