Some unexpected side-effects of the recent flooding are only emerging weeks later. Environment Correspondent Linda McKee looks at the aftermath of the deluge

The other day I settled down to a recording of Gardener’s World — a few weeks old — which included a brief weather forecast for the following day.

Although it warned to be beware of heavy rain, there was little indication of the devastation that would be wreaked on Northern Ireland — bridges and houses submerged, motorists swimming to escape their cars, the Westlink underpass filled to the lip.

Unexpected as those sights were, they weren’t the end of it.

Three weeks later and strange things are still being thrown up by the floods, even though the waters themselves have subsided.

If you’d been waiting on the banks of the Newry Canal or the Quoile last month, you’d have been forgiven for thinking the 10 plagues of Israel were upon us.

First the deluge, then the infestation of dead fish.

Initially there was shock that three major fish kills could have taken place within a week and it was assumed that man-made pollution was to blame. But then a more intriguing culprit emerged.

While one of the incidents was certainly linked to pollution, Northern Ireland Environment Agency officers investigating the fish kill at Moneypenny Lock in the Newry Canal gradually began to suspect another explanation as they were unable to find any traces of pollution in the river or its tributaries.

So far, the working theory is that the floodwaters stirred up the gunk in the bottom of the canal — mud gradually deposited over the years and devoid of oxygen.

That anoxic mud exerted an effect on the river very much like pumping a load of slurry or sewage outfall into the water — stripping the dissolved oxygen out of the water and suffocating the animals that make their home there.

Of these, the most obvious were the hundreds of fish gasping at the surface of the water but the incident will also have had an impact on the tiny invertebrates and bugs that keep the aquatic ecosystem healthy.

It can take years for rivers to recover from such incidents.

The reason why these fish weren’t killed straight away, NIEA says, is that the initial burst of floodwater brought masses of oxygen downstream and it was only later when the water calmed down that the problem with the mud started to emerge.

The organisation says something similar happened in the Quoile River in Co Down — hundreds of fish were killed by an increase in natural organic matter exerting a higher than normal pressure on oxygen levels in the water.

Social Development Minister Margaret Ritchie has called for a full investigation into the incident to discover the cause and find out how the fish kill could have been prevented. Could the Rivers Agency have taken any measures in the run-up to the flooding to lessen the impact, she is asking.

Geoff Nuttall, Northern Ireland director of environment group WWF, thinks not — but he does insist that we can take effective action if we think a bit further ahead. “To prevent the flooding in as short a space of time as a month or so might be asking a bit much. But thinking longer ahead there are ways to mitigate the impact of flooding,” he said.

“We are likely to face more flooding incidents in the future, given the predicted weather patterns as a result of climate change, such as more downpours which can lead to flooding.

“We can think about how we mitigate climate change but it’s also about how we adapt to it — that means trying to plan for flooding in a joined-up way, so that we plan our land use and development in a way that factors in the risk of flooding and also the effect on habitats.

“One of the issues is that some of our decisions have been made on one in 30-year flood incidents. The indications are that these are happening more frequently and therefore there is a need to update that. There’s always going to be flooding but we need the most up-to-date information on where that flooding is likely to happen.”