There are almost 20,000 lake names in Finland, and each of these names has a page in Järviwiki. On the name page you can find your lake on the map or by its municipality. Use the search to get to the right name page. You can also browse through all lake names on the Name category page.
The most common lake name is Mustalampi (Blackpond). As it is small lakes having names ending with -lampi (pond) dominate the list of most common lake names. In the top ten there are as many as seven of them. The most common name ending with -järvi (lake) is Saarijärvi on its fourth place.
Although, if the names were sorted according to surface area they cover, the list would look totally different. On top of that list you would find Saimaa, even though it is the name of just one lake - the largest in Finland.
Some lakes don't have a name at all (not in the lake registry anyway). In Järviwiki there are 13 642 of them, and they are labelled with Ei nimeä (No name). If you come across one of these lakes, and you know it has a name, be pleased to inform about the name at the discussion page of that lake.
Up to 16,048 lakes have a unique name.