Okoto (Rila)

How it formed

Okoto is a glacial lake in a cirque, a bowl cut by ice. It drains from its north-eastern end towards the lower lake Bliznaka. From the south a snowfield overhangs the lake, and its tongue very rarely melts away and stays outside the lake's outline. The streams from the Seven Rila Lakes are the source of the Dzherman river.

History

In 2005 two Bulgarian divers made the first dive into the lake in the history of Bulgarian diving, reached its deepest point and found that the depth had been increasing over the years. They donated samples of bottom sediment and water to the hydrobiology department of Sofia University.

The Eye

Okoto is at about 2,440 m, and its almost oval outline gives it its name, the Eye. It is the deepest cirque lake in Bulgaria, at 37.5 m. Of its neighbours, the Fish Lake is the shallowest of the group, at about 2.5 m, and the Lower Lake is the lowest.

Nature

It is the deepest glacial lake in Bulgaria, and one of the poorest in nutrients among the Rila lakes that scientists have studied, so its water is very clear and its food web short. The lakes usually freeze in October and do not thaw until June, under ice up to 2 m thick. The Rila lakes have been stocked for decades with brown trout and brook trout, and brook trout have been recorded here.

Around the lakes grows the Rila primrose (Primula deorum), a Bulgarian endemic found only on wet ground above 1,800 m in this range. It flowers from early June as the snow melts, alongside bird’s-eye primrose, alpine snowbell and the insect-eating Balkan butterwort. Since the chairlift opened in 2009, visitor numbers have soared, from 15,000 that year to 120,000 in 2011, and experts consider this too many for such a fragile place, so keep to the paths.