No swimming or fishing

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Re: No swimming or fishing

Post by exile » Mon Jul 15, 2019 11:32 pm

I think it is important to draw distinction between at least 3 different types of water contaminants described so far. I think we are in danger of confusing them and drawing wrong conclusions.

Sea lettuce - as described, lives in the sea. It can build up on beaches and then creates hydrogen sulphide as it decomposes (especially in Brittany for some reason). It is the gas released from the rotting sea lettuce that is dangerous, sea lettuce itself can be safely eaten, although in some areas it can become contaminated with heavy metals and consumption would not be recommended. I think this has already been pointed out but it does no harm to repeat it.

Chancer's canal weed - not possible to identify it from the description but this is clearly a plant or plants. One possibility is water hyacinth which becomes rampant in warmer weather - but it could be one of many. Most of these plants will be quite harmless, but if pulled out of the water and stored in heaps, there is a possibility that they will undergo anaerobic decomposition and create an unpleasant smell that is not generally dangerous. The same situation can occur in your garden compost heap if material packs down tightly in wet conditions so that air is excluded during the rotting process. Unpleasant but generally not dangerous. These plants have a tendency to block out light to the water beneath and through a series of processes the water becomes oxygen depleted and can easily end up with that stagnant smell.

Mysty's cyanobacteria - these are as described, bacteria and at very high concentrations they can form a scummy surface on the water. They do not form huge mats of material to be pulled out with a digger. The cyano bit of the name refers to the blue/green colour (Cyan) of the bacteria and has nothing to do with cyanide. Cyanobacteria can produce a range of toxins dangerous to man and these can be produced at dangerous if not lethal levels before there are major obvious visual signs of the bacteria (large scum mats on the surface) - so the water can look clear but be toxic. From Mysty's description that is where his lake is at just now.
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Le Démerdeur
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Re: No swimming or fishing

Post by Le Démerdeur » Tue Jul 16, 2019 12:08 am

An excellent posting Exile, what you described in your speculation sounds exactly like what I saw, I will get back there as soon as I can to get the name of the plant.

The smell and colour of the liquid that had started to leech out was just like that from a pile of silage (a clamp?) in a farmyard.

I definitely thought the cyan referred to cyanide so thanks for clearing that up.

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Re: No swimming or fishing

Post by rabbit » Tue Jul 16, 2019 8:55 am

Le Démerdeur wrote:
Mon Jul 15, 2019 9:50 pm
I ran along another section of the Somme canal tonight, maybe 20km downstream, clean as a whistle and no algue but on reaching the upstream ecluse there was a real pen & ink similar to the piles of removed vegetation, it happened immediately upstream of the ecluse where the flow of water is pretty much stalled, the section that was infested with the (what is the word in english i am searching for?) weed has several ecluses over a short distance so it clearly favours slow flowing or stagnant water.

Its a bit concerning because there is a club of mainly seniors who swim up to the ecluse I sniffed tonight at this time of year. They are a brave and hardy lot but it would not take a lot to incapacitate many of them.

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Re: No swimming or fishing

Post by Le Démerdeur » Tue Jul 16, 2019 10:29 am

No that's not the word in English I was asking for several times thanks, anyone know the word for floating weeds?

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Re: No swimming or fishing

Post by Annabelle's Papa » Tue Jul 16, 2019 10:37 am

FrenchForumSurvivor wrote:
Mon Jul 15, 2019 12:50 pm
Annabelle's Papa wrote:
Mon Jul 15, 2019 12:20 pm
Near us in Brittany it is pesticides leaking into the water source from farmers overuse for years, finally it hits the lake and when we get the really hot weather followed by the algae forming it causes a lethal concoction, that kills the fish, very large carp and zander can be seen floating and rotting on the surface. The commune a few years back, dredged the lake taking water out and into temporary man made lakes nearby and then returned to the lake, it took 18 months but the situation is vastly improved, as I write no algae in the lake today and the weather conditions at the moment are the ideal circumstances to cause it, maybe it has worked.

No swimming in our lake for 10 years now but it doesn't stop the kids jumping in.
Are you talking about Lac de Guerlédan, AP?
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