Several ridges in the Baltic were studied by means of diving. The dimensions of the ridges varied to a great extent and the ratios were mainly dependent on the thick-ness of single floes. In the skerries, where the ridges were formed from rather thin ice early in the autumn, they were relatively low and very often grounded. In the open sea, where the mobility of ice is more unhindered, the ridges consequently were larger in size. The biggest ridges found were lying against the fast-ice edge. The sail (the upper portion of the ridge above the water level) varied from 0.5 to 2 m in average. The keel (the lower portion under the water level) varied from 6 to 14 m in average. The maximum height of the sail was 3.5 m and the maximum depth of the keel was 28 m, but in this case the ridge was lying on the shore line, not in the open sea. Characteristic of the keel was that individual floes in a depth greater than 1 m below the sea level were not frozen together during the winter but remained loose. The spring melting usually starts at the bottom of the ridges very early in the spring.