Under the influence of the intermittent trade-winds Lake Nicaragua rises and falls regularly, whence the popular notion that it was a tidal lake.
The waters between these beaches and the mainland are gradually filling with sediment and changing into tidal marsh.
Arica has been three times destroyed by tidal waves, and other small towns of the north Chilean coast have suffered similar disasters.
The warping which is practised in England is almost exclusively confined to the overflowing of level ground within tide mark, and is conducted mostly within the districts commanded by estuaries or tidal rivers.
The sea pierces the islands in deep fjords, or separates them by narrow inlets through which tidal currents set with great violence, at speeds up to seven or eight knots an hour; and, as communications are maintained almost wholly by boat, the natives have need of expert watermanship. There are several lakes in which trout are abundant, and char also occur; the largest is Sdrvaag Lake in Vaagd, which is close to the sea, and discharges into it by a sheer fall of about 160 ft.
About one-eighth of the area consists of tidal marsh, lying chiefly between the long sandy ridges or barrier beaches of the Atlantic coast and the mainland.
A canal connecting the tidal part of the river Neath with the mouth of the Tawb, made in 1789, was in 1824 connected with the Vale of Neath canal by means of an aqueduct across the Neath river, when also a small dock, Port Tennant (so named after its owner) or Salthouse Dock, was made near the east pier, and this continued to be used till 1880.
Under ordinary conditions the sluices are raised to admit boats to pass from the half flood to half ebb, so that the river remains tidal up to Teddington, the next lock.
These exist for the purpose of regulating drainage, and providing defence against water in fen lands or lands subject to floods from rivers or tidal waters.
The mainland in the north and east is highly mountainous and forest-clad, and the lower portion is cut up into numerous islands by a network of tidal creeks.