Heddalsvatnet (English:Lake Heddal)^[2][3][4] is alake inNotodden Municipality andMidt-Telemark Municipality inTelemark county,Norway. The 13.2-square-kilometre (5.1 sq mi) lake is located just south of thetown of Notodden. The village ofHeddal and the Heddalen valley are located to the northwest of the lake.

Heddalsvatnet
View of the lake towards Notodden
Heddalsvatnet Location of the lake Show map of Telemark Heddalsvatnet Heddalsvatnet (Norway) Show map of Norway
Location	Notodden andMidt-Telemark, Telemark
Coordinates	59°29′40″N9°18′22″E / 59.49431°N 9.30623°E /59.49431; 9.30623
Type	glacier lake
Primary inflows	Heddøla, Hjukseelva, Klevaråa,Tinnelva and Tveitåa
Primary outflows	Saua
Catchment area	5,372.82 km2 (2,074.46 sq mi)
Basin countries	Norway
Max. length	16 km (9.9 mi)
Max. width	1.7 km (1.1 mi)
Surface area	13.2 km2 (5.1 sq mi)
Average depth	37 m (121 ft)
Max. depth	54 m (177 ft)
Water volume	0.44 km3 (0.11 cu mi)
Surface elevation	16 m (52 ft)
Settlements	Notodden
References	NVE[1]

The main rivers that flow into the lake are the riversTinnelva andHeddøla. Thecatchment basin covers a total area of 5,372 square kilometres (2,074 sq mi).^[1] The southern part of the lake is called Bråfjorden and is separated from the northern part by the Nautsundet strait which is crossed by the county road 360 bridge. The railway line to Notodden (theBratsberg Line) runs along the eastern shore. The villages ofHeddal andYli lie along the northwestern short of the lake and the villages ofHjuksebø andHjuksevelta lie along the eastern shore of the lake.^{[citation needed]}

The lake is part of theSkien watershed and is connected to the ocean by theTelemark Canal. Heddalsvatnet is only 16 metres (52 ft) above sea level and only two locks atSkien were needed to allow ships to sail on the lake. The canal opened in 1861 and made Notodden into Norway's largest fresh water port. In the late 1800s, seafaring vessels were constructed at the shores of Heddalsvatnet.^[5]

InNeolithic times, after the ice age, the ocean was about 150 metres (490 ft) higher in this area. Heddalsvatnet was a saltwater fjord connected to the ocean. The ocean stretched inland like afjord past Heddalsvatnet, all the way toHjartdal. The first humans in central Telemark presumably travelled by boat deep inland along the fjords that are now gone.^[6]

Post-glacial rebound eventually separated Heddalsvatnet from the ocean and turned it into a freshwater lake. As the ocean levels decreased, the lake became separated from the ocean around 1500 BC.^[7][8] The water in the lake gradually becamefreshwater around theBronze Age, according to archaeologist Pål Nymoen.^[9]