Weed Management

105 litres of blue dye have recently been deployed into the lake as part of 2013 fight against pondweed to give a concentration of 1 part dye to 5.75 x 10^6 water (this concentration should deter weed growth below about half a metre from the surface). We hope that the increased depth of water this year will mean we don’t need to harrow even our most vulnerable shallow regions. If anyone has access to a sensitive densitometer able to measure such turbidity would they please let Alan Dibble know.



Most inland fresh water lakes are subject to infestation by pond weed which can, on occasions, make recreational activity impossible, whether that recreation be fishing, sailing, power boating, skiing etc. In this paper the term “Weed” encompasses both plant and alga growths, i.e. plants that require sunlight and a supply of nutrients to allow photosynthesis for growth; note that alga can take many forms ranging from a green sludge to plant-like growths.

Most Sailing Clubs will have used several methods to combat excessive weed growth; these being:


Harrowing (from spring onwards),

Cutting (in the summer)

Without doubt, herbicides are the most effective control, but are now not available as they were outlawed by EEC in 2010. Hopefully, new, compliant herbicides will become commercially viable Summer cutting gives instant relief but leaves huge floating mats of cut weed to be removed or pushed to margins of lake.

Harrowing is also effective but once initiated MUST be rigorously continued throughout the growing season lest cuttings regrow; it is also a blunt tool as it destroys all habitats and inhabitants of the areas being harrowed In addition to pursuing these three practical options, MSC has been alert to other possibilities; for instance biological control using weed eating carp and colouring the lake to reduce sunlight getting to the plants to slow growth. Both these options were at the time discarded as impractical, but the 2010 ban on herbicides has brought the use of dyes to the fore with the knowledge that this method of weed control has been adopted with great success by commercial fish farmers. Recent advice is that dye concentration required is far lower than envisaged and that the purchase price of (food grade) dye is reasonable and competitive with other methods, and, as proved by the commercial fish farmers, there are no harmful side effects to fish, fowl, other wildlife or domestic animals or to the environment in general. Other approaches considered include Bacterial management and ultrasonic generators – these have not yet been trialled or investigated.

The full text of the paper is available for download here:
Dye use in weed management.