Ahti, called Ahto in the Kalevala so as not to be confused with the hero Ahti Saarelainen, is the Finnish water god, lord of lakes and sea, whose wife is Vellamo, mistress of the water. In fishing spells the two are asked to drive their 'cattle', the fish, into the nets, and the catch is his gift rather than a right. He is a master of the waters in the everyday sense of the fishing and sailing communities, not a remote cosmic power, and the tradition is carried by the spells and the runos.
Modern Practice
Ahti is asked at the water before lines go in - a pinch of salt, a coin, the first fish returned or a share of it - and thanked after. The practice is a fisherman's bargain with the one who owns the water, and it belongs to fishers, sailors and anyone who takes from a lake or a sea.