Aquatic toxicity right|thumb|Sea surface nitrate from the World Ocean Atlas In freshwater or estuarine systems close to land, nitrate can reach concentrations that are lethal to fish. While nitrate is much less toxic than ammonia, levels over 30 ppm of nitrate can inhibit growth, impair the immune system and cause stress in some aquatic species. Nitrate toxicity remains a subject of debate.
aquatic toxicity right|thumb|sea surface nitrate from the world ocean atlas in freshwater or estuarine systems close to land nitrate can reach concentrations that are lethal to fish while nitrate is much less toxic than ammonia levels over 30 ppm of nitrate can inhibit growth impair the immune system and cause stress in some aquatic species nitrate toxicity remains a subject of debate