At this time of year fish in lakes and ponds can suffer from low oxygen levels and unless the problem is spotted early enough large numbers of them can die.
Pollution, bacteria, sewage and agricultural waste can all cause de-oxygenation of a lake, but during the summer months, the commonest cause is the simple combination of water plants and the weather.
Environment Agency fisheries management officer, Jason Watts said: “In hot weather, aquatic weed and algae grow rapidly, giving off oxygen during the day and carbon dioxide at night.
“Normally, this means good oxygen levels in a lake, but if the weather turns cloudy, then the plants do not give off as much oxygen during the day and because it is still used up overnight levels can start to fall dangerously low.
“The fish are left with no oxygen and can often be seen gasping for air on the surface of the water early in the morning. If the problem isn’t remedied in time by aerating the water with pumps or compressors, many suffocate.”
Over the years, the Environment Agency has carried out a number of emergency fish rescues on lakes and ponds, but the Agency is often alerted too late. Jason Watts added: “We end up attending a fish kill. In some circumstances, the whole fish population has died.
“Different fish are able to survive lower levels of oxygen than others. Trout will suffer first, then roach and rudd and finally carp and tench. In extreme cases even eels have suffered.”
All anglers and the public can help prevent fish deaths. It is vital that action is taken as soon as any of the symptoms are noticed.
Anyone spotting fish in distress or gasping for air, especially early in the morning should immediately notify the owner or angling club. If that is not possible they should contact the Environment Agency as soon as they can.
Many of the causes, such as algal blooms, can be prevented with careful management but some are just down to nature. If any angling clubs or fishery owners would like advice or information they can contact their local Environment Agency Fisheries department.
Booklet
The Environment Agency has also now released an advisory booklet ‘ De-oxygenation, Practical Self-help For Fishery Owners and Managers’.
The booklet is intended as a simple guide for angling clubs and fisheries on the most common causes of low oxygen levels and ways to avoid and overcome them and is available free from environment Agency offices on 0845 933 3111.
If anyone spots fish in distress or dying they can contact the Agency on the emergency hotline number 0800 80 70 60.
