Final answer:
Lake Saimaa, the 4th largest in Europe, is located in Finland.
Step-by-step explanation:
The country that has Lake Saimaa, the 4th largest in Europe, is Finland.
Lake Saimaa is located in southeastern Finland and is the largest lake in the country. It covers an area of about 4,400 square kilometers and is known for its numerous islands and beautiful natural scenery.
Other countries in the region, such as Sweden and Norway, also have large lakes, but Lake Saimaa specifically is found in Finland.