The Hallwilersee is a lake in central Switzerland and is like the slightly further south Baldeggersee in the Valley. It is 8.4 km long, at its widest point 1.5 kilometers wide and up to 47 feet deep with an average depth of 28 m. Its area is 10.3 km ², of which five-sixths are in the districts of Lenzburg and Kulm in the canton of Aargau and sixth in the constituencies and high village Sursee the Canton of Lucerne. According to the size, it is ranked 16th of the Swiss lakes. The volume of the lake is 0.285 km ³, its catchment area 128 km ². The main inflow or outflow is the Aabach which opens at Möriken -Wildegg in the Bünz (which in turn nearly two hundred meters further flows into the Aare ). In addition, numerous small streams flow into the lake.
The Hallwilersee arose during the Ice Age, through the embankment of an end moraine. In cold winter weather, the lake can freeze. He was most recently in 1986 quite frozen. The village Hallwil is not on the lake, but about two kilometers from its northern end. The name of the lake comes from the Lords of Hallwyl.
The Hallwilersee is a popular destination for day trips. In the villages on the lake shore, there are numerous scenic restaurants and beach resorts. Also very popular is a hike around the lake, which takes about 4.5 hours. About one kilometer north of the lake is located on an island of Aabachs the water Hallwyl.
During the summer season drive various courses and extra ships of the shipping company Hallwilersee. Along the entire western shore runs the Seetalbahn the SBB ( Lenzburg Lucerne). The eastern shore is accessible by bus routes.
During the Mesolithic, the Neolithic and Bronze Age people lived in settlements on the lake shore Hallwilersee. In Seengen there was a settlement of the Romans. By 1300, the lake had different names: Halwiler se, lacus de Seingen ( to Seengen ) Escherse ( Aesch ). But then put the name of the bailiffs, the Lords of Hallwyl through. This possessed the high court and the court low over the lake and the fishing and navigation rights. The maritime court met on shore in Birrwil, Beinwil, Mosen and Seengen. From 1429 the buses were halfway to the fishermen.
Only in 1859 was the Hallwilersee to a publicly accessible waters. 1883 was the opening of the Seetalbahn along the western shore, 1888 took the excursion traffic with ships operating on.
Due to the extremely intensive agriculture around the lake with the appropriate use of fertilizers Hallwilersee was in the early 1980s, almost a "dead " lake. Because of the high proportion of phosphate were formed huge clumps of algae. The dead algae sank to the lake bottom and rotted there, while the there existing oxygen was consumed. Other aquatic plants and fish were thus not enough oxygen to survive. Since 1985, the lake is therefore artificially ventilated. In winter, compressed air is blown through nozzles at the bottom of the lake. Thus, the lake receives in addition to the natural circulation artificial circulation aid. Water is transferred from the deep to the surface, supplied with oxygen from the atmosphere. The fully -mixed lake is enriched with about 1,000 tons of oxygen.
In the summer the lake artificial oxygen is supplied. Pure oxygen is added directly on the lake bottom in fine bubbles the water. This 400-600 tons of gezehrten in deep water oxygen to be replaced. The heated surface layer of the lake will not be disturbed.
Through this artificial respiration, and by reducing the use of fertilizers, the phosphate content of the water was reduced from 250 mg / l (1975 ) to approximately 30 mg / l (2006) can be reduced.