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Lake weed "harrowing" to remove

T

Tim Walden

Senior Member
Lake weed - "harrowing" to remove

Hi Folks,

I've just heard that a local sailing club are going to remove the weed in a lake i fish by 'harrowing.' Having no idea of what this was, i went on to the Royal Yachting Assoication website below.

http://www.rya.org.uk/SiteCollectio...uments/Environment/RYA_Weed_Guidance_2011.pdf

Having read the document, it's basically a load of big chains dragged behind a boat that rip the bottom up. The idea is that it destroys weed growth and colours the water to reduce the amount of light that gets in.

My question is does anyone know what impact this will have on the fish and fishing?

Cheers,

Tim
 
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I would get a couple of rigs out to the area thats just been 'harrowed' as quickly as possible, as the fish will be checking out and feeding over the 'new ground' in the coloured water. In fact Mr. Hearn has written quite a bit on this very subject...

I don't know what it'll do for the long term prospects on your lake though, in my experience the weedier the better!

Nick
 
Tim Walden said:
My question is does anyone know what impact this will have on the fish and fishing.
Click to expand...

The fish will become extremely hungry and lose condition/weight.

The fishing despite what my previous statement might have you believe becomes damned hard. Juvenile tench will have lost there natural sanctury, so you'll land up catching some really small tench.
Carp (big) just seem to run scared and become very nocturnal in their activities, in daylight hours many will lie up in deep water. Depending on the lake depth, the shoals of carp can be easily located, just watch the coots, they become very wary of those areas and will not dive in them.

The cloudiness will fall out of the water quite quickly unless they are considering doing this on a regular basis.

All in all not a good move for either angling or the whole aquatic ecosystem.:(

Nick, normally the whole lake gets harrowed at once, we're not talking a bit of raking like is common practice when tench fishing, so where would you put your rigs?:D




An after thought; how about introducing a protected species like Greater crested newts, that'll thwart the boaters plans...;)
 
I'm sure I've heard that any piles of weed dragged in such a way that aren't disposed of properly, can become a pollution hazard if left on the banks.
 
All written vrry valid so far.

Difficult question without establishing age of water & existing nutrient loads either within the lake or inputs via streams etc being quantified. What is the depth & type of sediment? Has the water been prone to algal blooms in previous season? Has the water got any springs to cleanse the system? What is the proportion of bottom feeding fish to sliver fish? Is the water naturally turbid or relatively clear? etc...

As Colin mentioned, the colour from the dragging will quickly fall out of solution. However, the bed will have been disturbed which allows an accelerated exchange of nutrients to diffuse into the water column.

As the water warms up in spring, there will always be an initial algal boom which usually dissipates in a relatively short amount of time. However, as the amount of nutrients, especially bioavailable phosphorus concentrations will be greater this might compound their growth.

In addition, lack of larger plants means that competition for light & these nutrients will encourage greater densities of algae. This is usually a slippery slope to eutrophication or higher states of eutrophication, the extent of which will only able to be seen in the summer.

Essentially loss of habitat will always effect diversity & abundance of species of all trophic levels.
 
Hi Folks,

A bit more detail. When this has been carried out on ther lakes in the past the whole lake has been treated in one go. The advise from the RYA is to start in February and carry out a raking every 6 weeks. Historically the lake was very weedy, but has been treated for several years until those chemicals were outlawed. When they were used there was always some weed left around the edge. The lake is 3 - 9 feet deep, crystal clear, alomst devoid of small fish and is pretty much populated by predators and bottom feeders.

There is no spring feeding the lake, and the algae that has been present in the past has been the green 'slime' type.

Cheers,

Tim
 
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