Vltava in Prague safe for swimming, says expert
The city of Paris spent huge amounts of money ahead of the Olympics to make the River Seine safe for swimming. Unlike the French capital, Prague already has several public bathing spots along the Vltava. Does that mean that swimming in Prague poses no risk? I discussed the question with Tomáš Hrdinka of the T.G. Masaryk Water Research Institute,
“I can say that swimming in the Vltava in Prague is generally safe. The Vltava River has a much better starting position than the Seine, because a substantial part of the water comes from the lower outlets of its cascade reservoirs.
“This water is generally very cold, around 8 to 10 degrees Celsius, and is free of bacterial pollution and cyanobacteria that cause most problems associated with river pollution. Air oxygen is very well dissolved in this cold water, which further helps to break down possible organic pollution.
“While the Sázava and the Berounka, the main tributaries of the Vltava, do bring some pollution, the water quality of the Vltava remains at level two or three on a five point scale throughout the year.”
How has the quality of water in the Vltava changed over the past decades?
“Over the past 30 years, almost all Czech rivers have significantly improved their quality. The improvement was mainly driven by the construction and modernisation of waste water treatment plants in small towns. What also helped to clean the water in Czech rivers was the connection of small municipalities to the sewerage system.”
What are currently the biggest sources of pollution? Is it the small municipalities that you mentioned or is it something else?
“As you said, the biggest source of pollution today are small villages that are not yet connected to sewers and also discharges from the waste water treatment plants, including the new ones.
“That’s because most treatment plants in Europe, including Czechia, still don’t have a so-called quaternary cleaning stage, which gets rid of micro-pollutants, such as pharmaceuticals, drugs and hormones that are released into rivers and can affect aquatic life.
“Water quality can also temporarily deteriorate after heavy rain when treatment plants higher up in the catchment can be washed away or sewerage system can be overloaded with polluted water, which goes straight to the rivers.”
So what would you say are the biggest health risks associated with swimming in the Vltava these days?
“Like I said, it is faecal bacteria and cyanobacteria. Faecal bacteria such as E.coli may cause stomach or digestive problems if the water is ingested, while cyanobacteria can cause rashes or eye inflammation.
“That’s why their maximum concentration in the water is regulated by legislation. In the case of the Seine, the faecal bacteria limit was exceeded several times before the triathlon race could finally take place.”
The tri-athletes who swam in the Seine complained about an incredibly strong current. Could that also be a danger in the Vltava?
“Yes, of course. In the Seine, the flow is now much greater than is usual for this time of year due to the heavy rains. Something similar could also happen in the Vltava during the floods.
“But unlike the Seine, the Vltava has cascade reservoirs which reliably capture smaller floods and therefore the flow in the Vltava River is more balanced throughout the year than in the Seine. However, swimming in rivers is generally prohibited during floods because of the high risks.”
