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Consistent oxygen levels during spells of hot weather will improve the carp fishing for summer anglers

fishing lake with new aeration system

The importance of oxygen

Just like us, carp need the right environment to grow and prosper and that includes sufficient levels of oxygen in the water. In the winter, the oxygen levels are naturally high as cold water holds more oxygen than warm. As the year progresses and the lake temperature rises, there is less oxygen available to the fish.

During long periods of hot weather, algae can thrive. During the day, the water becomes oxygen rich thanks to the algae but at night the levels can drop dramatically. This leads to large differences between the day time and night time levels which makes it harder for carp to digest food.

At some point during the algae life cycle, it will die (known as a crash). This process consumes massive amounts of oxygen and can strip up to 100% of the oxygen, potentially killing all the fish.

Doing the right thing for the fish and for our visitors

If you came to see us before 2015 in the summer, you’re bound to remember the very loud fountain type aerator that would make you jump 5 times a day when it switched on. We’ve since relied on a silent sub-surface aeration system but on its own, it just isn’t powerful enough to stabilise the whole lake. We still use the fountain aerator occasionally when it’s really necessary.

Like many other lakes, we’ve now installed a bottom diffusion aeration system. The main principle is that each diffuser head brings the low oxygen bearing water to the surface so it can absorb oxygen from the atmosphere. The system is now powerful enough to circulate the whole lake twice every 24hrs. The pump is located on the island and is very quiet! You’ll also notice 6 diffusion heads spread around the island in a way that should not interfere with the fishing.

The technical bit

At the heart of the installation is a super quiet (45db) linear diaphragm air pump. This supplies air at 0.15 bar at a rate of 300 litres per minute to the pressured ring main that runs all around the island margin. Six valves on the ring main supply air to self sinking air hoses. At the end of each 10m hose, there is a self sinking low-profile cylindrical diffuser head. The heads themselves vary from 500mm to 1000mm in length depending on the depth of water and the makeup of the bottom. The heads produce up to 18000 bubbles which range in size from 1 -3mm.

The bubbles have a massive surface area relative to their volume which means that more low oxygen water molecules are exposed to each tiny air bubble. The secondary effect is that as the bubbles rise, they push water from the bottom of the lake to the top and expose even more water molecules to the air, thus oxygenating them.

Each diffuser head is basically a re-circulating water pump, powered by air. The system re-circulates 18000 m3 of water every hour which means that the water in the lake gets turned over twice every 24hrs.

What it means for the fishing

  1. Stable oxygen levels will accelerate fish growth rates meaning larger specimens for the photo album and fewer tough weeks when bites are hard to find no matter what you do.
  2. The old aerators only provided increased oxygen levels in the shallow end of the lake. Now, the oxygen levels are better distributed throughout the lake and we expect more consistent catches from all swims.
  3. With more oxygen available, the carp are eating more! Given sufficient oxygen (70%) and an average water temperature of 25 degrees (which we currently have), carp can eat 3% of their body weight of food per day. For Beausoleil, that means 30kgs a day for the carp alone!
  4. Algae does not like to be moved so in a lake where the water is constantly being circulated the water clarity should slowly improve over time which will produce darker carp which everyone loves!

Gathering the data

As our visitors know, I now take readings three times a week at 9:30am when the levels are naturally low. The system has been in operation for a month and during this time we’ve seen a steady increase in the oxygen level. The average reading since installation has been 72% which is excellent.

  • For good growth, carp need 6mg/l of oxygen, approx. 70% saturation. Below this level the carp feed less and are simply harder to catch.

On a sunny day, the oxygen levels climb higher and the lake can become super saturated. The result has been heavy and prolonged feeding periods with the carp eating everything that they can.

We’ll continue to monitor the levels very closely and update our visitors on the lake conditions week in week out.

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