The rich and diverse wetland area of Siikalahti was formed as a result of lake drainage carried out in the 19th and 20th centuries. The surface was purposely lowered by 3 metres. 56 sq. km of the former lake bed was then used as farmland.

Over the decades, the open water areas have significantly decreased. In the 1940s, Siikalahti’s open water surface was four times larger than it is today.

The shallow, lush bay of Lake Simpelejärvi is naturally overgrowing. This has been caused by the shallowness of the bay, the surface of the lake being dropped, the waste water which was dumped into the bay in the 1960s and 70s and nutrients which have seeped into the bay from surrounding farm fields. Ditches dug at the south end and west shore of the bay during the mid 1980s impaired living conditions for birds permanently.

Restoration of the wetland began at the end of the 1980s. An embankment and a dam were built around the south part of the bay. The flues around the dam pump runoff waters into the bay. The embankment and dam has made it possible for the surface of the southern portion of the bay to be 40 cm higher than the rest of Lake Simpelejärvi.

A certain phase when the wetland is overgrown makes it the ideal habitat for wetland birds, so Siikalahti requires care and management constantly.

There is a long tradition of monitoring the bird population at Siikalahti. A register of the area's birds has been kept updated since the late 1940s. The species and individuals have been counted nearly every year since the late 1960s and are therefore comparable. This is a record in Finland as no other area has lists from such a long period. Studies have also been carried out to find out the effect of ditching, changes on shores and different types of management have on the bird population.

During the time that birds have been registered on sighting lists about twenty news species have started to nest at Siikalahti. Only a few species have disappeared from the area during this time. The changes in bird population are due to open waters becoming overgrown by vegetation, shore meadows becoming larger and new shrubs taking over the area. Bird species have changed cyclically in the whole of southern Finland and this too has played a part. Other things that are monitored closely in the area are changes in vegetation and the quality of the area's waters.

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