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Warm May weather means fewer mosquitoes, but more algae

Toxic blue-green algae blooms will make an earlier entrance to Finland's waterways this summer, but recent dry conditions will also result in fewer mosquitoes.

Sinilevälautta Taipalsaaren Saimaanharjun venerannassa 30. kesäkuuta 2016.
A blue-green algae bloom Image: Johanna Luukko/Yle
Yle News

Warm May temperatures mean that blue-green algae, the scourge of millions of avid lake and sea swimmers in Finland, will appear two to three weeks ahead of schedule this summer.

The abnormally sunny and warm weather is expected to last for at least another week, maybe longer, providing the perfect conditions for the algae to grow quickly. Blooms cover the surface of the water and can make it look like pea soup.

"Usually the first blue-green algae sighting are made around Midsummer, but now they might be upon us already in early June. This means they could appear two to three weeks earlier than normal," says Finnish Environment Institute (SYKE) unit head Marko Järvinen.

He says people with homes or cottages near the shoreline should prepare to see the algae already before Finland's Midsummer holiday, which falls on the third weekend in June.

"I don't recall it ever being this early. This means we will start checking the coasts for blue-green algae in just a few weeks," says SYKE lead researcher Harri Kuosa.

Kuosa says that the first blooms of the toxic algae will occur in the shallow bays off the Gulf of Finland, but that the entire southern coast, the Archipelago Sea and the Bothnian Sea are at risk.

Among Finland's tens of thousands of lakes and rivers, the first that will be see blue-green algae blooms form will likely be those that are nutrient-rich and feature an overgrowth of plants. These are most prevalent in the inland waterways of southwest Finland.

SYKE will start regular updates on the blue-green algae situation in Finland on June 7. Monitoring will continue until at least August, with new reports published each Thursday.

Avoid drinking or washing with algae-infected water

Home and cottage owners can also do their own test to measure the amounts of algae in the water by simply taking a sample in a pitcher and letting it stand for an hour or so. The bacterial algae in the sample will rise to the surface in this time.

If there is as noticeable amount of blue-green algae in the water, it is best to avoid drinking it and using it for washing clothes or dishes or bathing. Authorities advise against using it to create steam in sauna as well. If you chose to swim in the water, rinse yourself off carefully with fresh water after your dip.

Some blue-green algae blooms can produce chemicals that are poisonous if swallowed by people, pets, or livestock. Examples include neurotoxins that affect the nervous and respiratory systems, and hepatotoxins that affect the liver.

Symptoms brought on by exposure to blue-green algae include itching, burning and other forms of skin irritation. In some cases, it can even cause nausea and vomiting. Medication for pain and fever relief can often be of assistance.

Dry conditions cut mosquito population

A warm and dry start to the summer might bring good news, too, as the number of mosquitoes will drop if things stay dry for a couple more weeks. The pests need humid conditions to evolve, and if the larvae don't get a good dose of rain soon, they will die.

"It all depends on moisture levels in the spring. But this year it looks like there will be fewer mosquitoes than normal," says Reima Leinonen, an entomologist with the Kainuu ELY centre.

Unfortunately, even the drier conditions can't save the residents of northern Finland, because the high number of swamps and bogs that stay wet through the summer in the north provides the perfect breeding ground for the insects.

"Wetlands always produce plenty of mosquitoes to torment us," Leinonen says.

Less does not mean none, either. Even in southern areas, there are plenty of wet areas for mosquito eggs, larvae and pupae to grow. Because all of the first mosquitoes of the season reach their adult stage at the same time, it may seem as if there are swarms of them, even in areas that have been dry and warm.

"Because all adult mosquitoes emerge at the same time, it may seem like there are a lot of them flying around at first," says Leinonen.

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