Many rivers flowing into the Sea of Azov form bays, lagoons and limans. The sand, silt and shells they bring are deposited in the areas of reduced flow, that is the sides of the bays, forming narrow sandbanks called spits. Typical maximum depth in the bays and limans is a few metres. Because of shallow waters and abundant rivers, the spits are remarkably long and numerous in the sea – the Arabat Spit stretches over and is one of the world's longest spits; three other spits, Fedotov Spit, Achuevsk Spit and Obitochna Spit, are longer than 30 km. Most spits stretch from north to south and their shape can significantly change over just several years.