April showers bring, well, you may not want to know.

Heavy rainfall this spring is fuelling more human sewage pollution of the Thames River from London, a problem linked to the explosive growth in recent years of life-killing toxic algae in Lake Erie, into which the Thames ultimately flows.

In the first three months of 2016, figures reported by the city on its website show London dumped 59,473 cubic metres of raw sewage into the river from its waste water treatment plants and 91,171 cubic metres of partially treated waste.

That sewage — from so-called “bypasses,” when heavy rains overwhelm the system — was enough to fill about 60 Olympic-sized swimming pools.

“That seems high to me,” said Mark Helsten, a senior water resources engineer for the Upper Thames River Conservation Authority. “We have had a lot of rain and run-off, the ground is saturated and if we get any rain now the system is overloaded.”

Much of that overflow was from March, when sewage flowed on 16 separate occasions when London was hit hard by rain.

The Thames flows into Lake St. Clair, which drains into Lake Erie.

Algae blobs in Erie, fuelled by phosphorus found in farm run-off and industrial and human waste that drains into the lake from both sides of the Canada-U.S. border, have ballooned in recent summers, with one growing to the size of Prince Edward Island a few years ago.

When it dies, the decomposing algae sucks up so much oxygen it contributes to so-called “dead zones” in the lake where nothing lives.

While London draws its drinking water from both Lake Erie and Lake Huron, the greatest concern is the toxic algae in the lakes, to which city pollution contributes, Helsten added.

“We need a few weeks to dry out,” he said. London also needs better sewer infrastructure to handle the overflow, he added. But that’s a slow and costly process that involves separating older combined storm and sanitary sewer systems in many neighbourhoods.

Improvements are “a long way off, it takes time, maybe we need to pressure other levels of government for support on this,” said Helsten.

In fact, improving the sewer systems to ease the problem may take 30 years, said Geordie Gauld, the city’s division manager for waste-water treatment.

“I am not saying you should not be concerned — it is a larger amount than anyone wants it to be,” he said of untreated waste flowing into the river.

The solution lies in separating connected storm and sanitary sewers. The city is doing that work in neighbourhoods, as it does road work, but it will be decades until most are done.

“The (sewage) plants have capacity to sustain an average type rain without overflow,” said Gauld

“It is going to be a gradual process, these issues are buried well below the streets.”

There were no bypasses in the first three months of last spring, since it was cold with little rain. But the city was hammered by heavy June rains that caused many homes to flood, with sewage flowing into the Thames 25 separate times that month.

Helsten fears climate change is causing heavier rainfall and the problem will only intensify in future years.

“We are seeing more frequent weather events. Anecdotally, we know that is happening. We have not had springs like this with heavy rain and now snow,” he said.

Ontario and Ohio have committed to reducing phosphorus levels going into Lake Erie.

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WORST DAYS

Human waste discharged into the Thames River in London

2016

March 31: 23,848 cubic metres, Pottersburg waste water treatment plant. Untreated.

March 31: 23,268 cu. m, Dingman pumping station. Untreated.

March 31: 62,265 cu. m, Greenway waste water treatment plant. Partly treated.

2015

June 27: 108,858 cu. m, Greenway waste water treatment plant. Partly treated.