The Reuss weir is one of the last remaining needle dams in the world. What's a needle dam? It's a weir, which maintains both the water level and the flow of the river through a series of thin pieces of wood, often called needles. You can tame the flow of the river by adding or subtracting these needles. It was built in 1859 by the French architect Chuaree and in 1998 the hydroelectric power plant was completely redesigned and equipped with the latest technology available. It produces 4.3 million kWh per year, which is enough to power around 1,500 households in Lucerne. Between 2008 and 2011, the weir underwent a 23 million Sfr renovation, which resulted in greater flood protection for the lake and the River Reuss, preservation of the listed needle dam, better living conditions for plants and animals and the continuation of energy production. The water level of the lake can now be maintained at an optimum height regardless of weather conditions. No swimming is permitted between the Chapel and Mill bridges, but if you're lucky you might catch sight of surfers on the other side of the Mill Bridge on a hot summer day.