Why Have Fish Died In My Lake?

Much like humans, fish require oxygen to survive but unlike the atmosphere we breathe, a body of water contains a fraction of this oxygen content so this balance is more critical.  It is therefore crucial to manage the water by introducing and maintaining a means of circulation and aeration.  It can be a very upsetting sight to see a number of fish floating on the lake surface and the primary cause is usually oxygen depletion.   Once a fish kill has taken place, there is little that can be done aside from emergency aeration, which may be too little, too late.  However, the lake is expressing signs that there are issues and these should be addressed sooner than later to safeguard longer-term.

Oxygen Reduction Or Depletion

A very visible sign of oxygen depletion is fish gasping or acting erratic at the lake surface, as they try and pull oxygen which is no longer present in the water. Plants, beneficial aerobic bacteria, fish and other aquatic life will all be competing for oxygen.  As the water temperature rises, its ability to support oxygen reduces compared to the cooler winter months so any issues will be exacerbated during the warmer seasons. 

Virtually any pond or lake will benefit from aeration and this is a highly effective strategy for long-term preventative care.  A Floating Fountain or Lake Aerator will have a huge impact on maintaining oxygen levels for all pond inhabitants and beneficial aerobic bacteria will thrive and gradually reduce organic waste on the lake floor.

Parasites & Disease

Try to inspect one or more of the fish which have died.  Are there any signs of disease or parasites?  If disease is apparent but difficult to identify the exact cause, contact a fish health specialist who should be able to identify the issue via photographs or a sample.  They should also be able to recommend a treatment or strategy to address the underlying issue. 

Pesticides & Run-off Pollution

If the dead fish seem otherwise healthy, test the water for any fluctuations in pH or spikes in ammonia, ammonium and nitrite.  If the surrounding lake is agricultural, is the land being treated with pesticides?  If so, this could be leaching into the lake and affecting the water chemistry.

Please feel free to Contact Water Garden Ltd for further advice on any pond or lake issue and we’ll be happy to assist.