Artificial lakes serve many purposes

What is the point of constructing artificial lakes in Finland? We already have tens of thousands of lakes. Why have artificial lakes been constructed, and how many are there?

The oldest artificial lake in Finland is located in Orisberg, Isokyrö. It was constructed in 1783 to provide the local ironworks with a steady supply of hydropower throughout the year. When electrification began in Finland later, new artificial lakes were created to support hydropower generation.

Other important reasons for constructing artificial lakes include flood protection and domestic water supply. Some have also been constructed for recreational use; if there are no lakes nearby, an artificial lake may have been constructed to provide a bathing area.

There are some fifty lake-sized artificial water bodies in Finland, the largest ones being Lokka and Porttipahta in Sodankylä. Additionally, there are countless artificial ponds and reservoirs.

Artificial lakes are usually created by damming rivers or by cutting off a sea bay. Many started life as smaller lakes: the water level was raised until the surface area of the lake was many times the original size. Others were created by building an embankment on dry land or in a mire, for example. A sand pit or quarry may also have turned into a lake almost by itself.

Many old artificial lakes have become landscape features over time. They have developed characteristic lake ecosystems, and littoral vegetation has established itself. On the flip side, naturally valuable areas have been lost. The ecosystem of an artificial lake serving as a reservoir may also be adversely affected by unnaturally large water level variations that differ from the natural rhythm.

Image: Hannu Vallas