What can cause this smell in a stream

[Stinky Bob]

On my morning walks there is a small stream that feeds a big pond/small lake, at the other end of the lake the stream emerges for about 10 feet then goes under the lane and feeds another small lake on the other side. Recently I have noticed that the stream between the 2 lakes has a white film on its bed, the stream at this point is flowing downhill over rocks and is only about 3" deep. There is also a sulphorous/bad egg smell. DOes anyone know the likely causes of this. Both lakes have a large amount of blanketweed covering them and I was wondering if the issue was caused by lack of oxygen killing of the lake plant llife and this rotting down and being washd along the stream. Going back to where the first lake is fed and about 50 yards from this stream is a very small industrial estate with a Aluminium fabricators and powder coating company, the stream by this company is slow moving and murky but there isn't any smell. Any tips would be welcome

[valleyforge]

Hi Stinky Bob,

The sulphurous/bad egg smell is due to the liberation of Hydrogen Sulphide, a poisonous, heavier-than-air gas, which is caused by the anaerobic (in the absence of air) decay of organic material ... most probably by bacterial action.

Although H2S gas is toxic in even small doses, it is very hydrophilic ... that is, it combines very readily with water (to form dilute suphuric acid), so in an open air/water environment it shouldn't reach dangerous levels of toxicity although the smell can be pretty bad.

Incidentally, with increasingly higher H2S concentrations your nose very quickly becomes desensitised to the odour, which of course makes it all the more deadly.

A fitting post from someone with your handle, Bob.

[Stinky Bob]

Hi VF,
thank you for that answer, would you say that the blanket weed covering is the most likely cause, the lakes are on private property so cannot check for aquatic life but there is a reasonable amount of bird activity, a few swans and migrating geese etc.

[valleyforge]

It's possible I suppose that the breakdown of the blanketweed is what's producing the gas, but more usually H2S is liberated from the products of subsurface decomposition ... so maybe something has stirred up the bottom of the lake(s)?

I would guess that the white film in the stream bed between the lakes is quite possibly dead blanketweed though ... dead/dried algae does appear white or silvery.

Blanketweed is often successfully tackled by the enzymes in barleystraw ... submerged bundles of this can be used to help keep garden ponds clear, but it would be beyond my direct experience I'm afraid to advise how it could be effectively tackled on a large lake, especially if it's on private land.

Perhaps some other member(s) will be able to advise further?

[Stinky Bob]

Thanks again VF,
I suppose my main concern is that it wasn't the industrial unit that was causing the problem, not that I know it is a problem, just that I havent seen it before in the 5 years that I have lived here.

[Cotham Marble]

Originally Posted by Stinky Bob

Thanks again VF,
I suppose my main concern is that it wasn't the industrial unit that was causing the problem, not that I know it is a problem, just that I havent seen it before in the 5 years that I have lived here.

This is certainly worth a call to your local Environmental Health Dept. They will investigate, and where necessary involve other agencies. There may be an entirely 'natural' explanation for what is happening however from your description a human impact seems most likely.

CM

[excoriate]

Echoing the poster above, definitely report it.

The streams where I used to live were often the victims of poo spreading. The water turned grey, there was a white film on the rocks and it smelled bloody awful.

So if its not something natural breaking down, it could be a release of some sort.

Good luck

[Stinky Bob]

Thanks everyone for their comments, intialy I was going to leave it for a week before talking to the EA but today the smell has got slightly worse. So I will give them a call.