Morské oko (called Veľké Vihorlatské jazero in the past; literally "Eye of the sea") is a lake in the Vihorlat Mountains in eastern Slovakia.

It is at an altitude of 618 m, covers 0.13 km² with a maximum depth of 25.1 m. It is drained by the river Okna.

The oldest known description of the lake can be found on two maps, dating back to 1687.

In the past, rainbow trout (Oncorhynchus mykiss) was introduced into the lake, but the prevailing species today is the common chub (Squalius cephalus).

It is a national nature reserve (covering 1.08 km²) since 1984 and part of the Vihorlat Protected Landscape Area.