A small group of rocky islands, Formiche di Grosseto (42°34′2N, 10°53′2E), lie 7.5 miles offshore. The group comprises Formica Grande, the largest and highest (elevation 12 m); Formicca Picola the middle islet, dark coloured with an above water rock close E of it; Formica III is the most S of the group. The channels between the rocks have depths of less than 10 m and are dangerous. A shoal with a least depth of 3.6 m over it lies close N of Formica Grande. A bank with depths of less than 9 m extends 280 m S of the rock; fishing vessels sometimes shelter here. Formica III, the S rock, stands on rocky bank extending up to 320 m from it; the bank has depths of less than 9 m over it. During gales overfalls develop up to 0.6 mile S of this rock.