Once it reaches the southern tip of Laos, the course of the Mekong widens, in places reaching a width of up to 10km during the height of the wet season. During the dry season, the drop in water level results in the reappearance of myriad islands (don), islets and sandbanks, collectively known as the 4 000 islands, or Si Phan Don. Some of these are used to grow crops or set aside as grazing land for water buffalo. Only a handful of permanent islands are occupied by small hamlets (ban) with their traditional wooden houses.