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International Society for Infectious Diseases <http://www.isid.org>

Date: Tue, 4 Sep 2012
Source: The Windsor Star [edited]

A strong sewage smell preceded scenes of dead fish littering the shores of Lake Erie this weekend [1 - 2 Sep 2012] and has residents wondering what caused the massive die-off, the president of the Rondeau Cottagers Association said Tuesday [4 Sep 2012].

"This is a very substantial fish kill and there's something really wrong to have a fish die-off like this," said Dr. David Colby, a cottager who is also the Chatham-Kent medical officer of health.

Colby said it is more of an environmental disaster than a threat to human health since it would be foolish to eat dead fish from the shore. He's waiting to hear results from the Ministry of Environment, which collected fish and water samples Saturday [1 Sep 2012] that could take a few days to analyze.

He said some of the possible causes for the fish die-off wouldn't explain the smell which started Friday [31 Aug 2012], peaked at 3 a.m.
Saturday and wasn't like the rotting fish smell that has taken over the shoreline.

"All kinds of people were woken out of a sound sleep by a stench and it was like a septic tank was backing up," he said.

Colby said he's never smelled such a sewage stench on the lake and he's never seen anything like the scenes of large dead fish littering the beach.

Ministry of Environment (MOE) officials aren't sure what killed the fish, but preliminary tests and observations ruled out pollution or spills, MOE spokeswoman Kate Jordan said Tuesday [4 Sep 2012]. There was a strong manure smell Saturday [1 Sep 20122] but Jordan said there was no sign of manure runoff.

"Certainly all the field measurements that our staff did on the weekend as well as observations that they made didn't point to or indicate any source of spill or man-made pollution," Jordan said.

A significant number of dead fish in the tens of thousands was reported to the ministry on Saturday in a 40 kilometre stretch from Rondeau to Duttona Beach which is west of Port Stanley in Elgin County, she said.

"Natural causes are a possibility. We are considering the possibility of a lake inversion," she said.

Jordan said that is a flipping of the lake water when there's a temperature change. She said it was windy and choppy the night before the fish die-off. The top layer of the lake gets colder than it would normally be and it sinks and the colder water at the bottom of the lake with low oxygen levels moves up. Jordan said that could kill the fish. The Ministry of Natural Resources is also looking into the dead fish.

Colby said he didn't think the water temperature had dropped substantially and that wouldn't explain the sewage smell.

Oxygen depletion usually causes these kinds of fish kills and that could be linked to algal blooms, which haven't been seen yet in that part of Lake Erie, to high water temperatures or sewage runoff, Colby said.

He said there are other possible causes for the dead fish such as a fish disease called viral hemorrhagic septicemia and Type E botulism, a bacterial toxin which would kill birds that feed on dead fish. He said he's already seen a sick gull near the dead fish but that is not conclusive evidence. The disease or toxin that could have killed the fish would present no hazard to humans, he said.

Communicated by:
ProMED-mail from HealthMap Alerts

[A naturally occurring temperature inversion might bring an oxygen-depleted layer of water from the bottom of a lake close to its surface. The density of water depends on its temperature, and water is at its densest at around 4 degrees Celcius (39.2 Farenheit). Water that is colder or warmer than 4 degrees will be 'lighter', and will tend to move upwards. This property of water makes it tend to form into layers. In a lake, the interface between those layers will know as a thermocline. If water at the surface changes approaching 4 degrees celcius it will sink downwards. Changes in temperature of deep water can occur (say from geothermal inputs), but they are quite rare.
The rotten smell might originate from anaerobic digestion occurring at the bottom of the lake, which might produce the bad smelling and lethal hydrogen sulfide. Gases like hyrogen sulfide might also originate as a natural gas from the depths, so a geologic input should not be ruled out.

A more recent news release
support the hypothesis that the fish died due to an oxygen-depleted layer of water.

A map of the affected area can be accessed at:
<http://healthmap.org/r/3mvT> - Mod.PMB]

[see also:
Die-off, fish - USA (06): (OH) RFI 20120827.1266581 Die-off, fish - USA (02): (GA) comment 20120601.1153265 Die-off, fish - USA: (GA) pollution susp. 20120531.1152141
Undiagnosed die-off, fish - USA (02): (GA) columnaris 20110528.1641 2010
Undiagnosed fish die-off - USA (04): (WV, OH, PA) columnaris 20100610.1946] .............................sb/pmb/mpp/ll
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