 Silt deposited by this process forms into long narrow banks which run many kilometres.The silt was deposited over the past 10,000 or so years - since the end of the last glaciation and the rise in sea levels that flooded the Gippsland Lakes - to form silt banks or islets as the speed of the river slows.The silt jetties have been nominated by geologists as a site of international significance, second in size to those of the Mississippi River at the Gulf of Mexico.