Final answer:
The Mar Menor lake is located in Spain, within the region of Murcia, and is separated from the Mediterranean Sea by the strip of land called La Manga.
Step-by-step explanation:
The country that has the Mar Menor lake is Spain. Mar Menor is a coastal saltwater lagoon located in the Iberian Peninsula in the southeast of the Spanish region called Murcia. It is separated from the Mediterranean Sea by a narrow strip of land called La Manga, which is approximately 22 kilometers in length. The Mar Menor is known for its high salinity and the area is a popular destination for recreational activities such as swimming, sailing, and watersports.