After the ice age, Granvin Fjord reached all the way up under Skjervsfjossen waterfall. Just a thousand years later, as a result of the rising of the land after the ice melted, this whole inner part of the fjord freed itself of the sea and became Granvinsvatnet lake. In spite of this rise in elevation, this waterway is still navigable for fish: Sea trout have wandered into Granvinsvatnet in more recent times and evolved to become freshwater trout. And salmon and sea trout made the journey 13 kilometres up the Storelvi river.
Early in the 1900s there were much larger salt water deltas in Hordaland. But, essentially all of the larger river deltas got filled in and regulated for use in industry during the last century. Now, there is only Haugsdals delta left.
During the latter half of the 1900s the big natural river deltas on Westland disappeared. Until the 1980s there was still a small, but significant remnant of the original river delta from the Etneelva river, but today most of this, too, is industrial land.
The Strandaelvi river is forever protected from the development of hydropower. The Lønaøyane islands – which comprise the delta furthest north in Lake Lønavatnet - are a part of this water system. In 1995 the level of protection for the Lønaøyne islands was strengthened to that of a nature preserve because of the rich birdlife in this wetland.
Mykdal delta had an unusually diverse bird life, right up until 1987. The Myrkdal delta should have been protected, and the plans were prepared. Despite the area's high elevation at 227 m a.s.l., it had a wide variety of bird species compared with other fresh water wetlands in inner Hordaland. Several of the bird species were also unusual for the region. The delta had for example a permanent nesting colony of Eurasian Wigeon, believed to be the only one of its kind in the municipality.
The sediment that was deposited from the river Dyrvo has created the fan-shaped delta Rekvesøyane. The bit of land farthest out toward the water gets periodically flooded, especially during snow melt and after periods of much rain.