Lake Tuusula or Lake Tuusulanjärvi (Finnish: Tuusulanjärvi, Swedish: Tusby träsk) is a lake on the border of the municipalities of Tuusula and Järvenpää in Southern Finland. The lake has an area of 6.0 square kilometres. Since the beginning of the twentieth century the shores of Lake Tuusula has been an artist's colony. The houses of Jean Sibelius,Juhani Aho, Pekka Halonen, Eero Järnefelt, Joonas Kokkonen, and Aleksis Kivi are on the edges of the lake.
The Lake Tuusulanjärvi Water Protection Association has taken action to save the lake from eutrophication effects since the early 1970s. Apart from wintertime water aeration and cyprinid fish removal, some additional water is being fed into the Lake via the Päijänne Water Tunnel.
Tuusula (Finnish pronunciation: [tuːsulɑ]; Swedish: Tusby, [ˈtʉːsbyː]) is a municipality of Finland. It belongs to the Helsinki sub-region of the Uusimaa region. The municipality has a population of 38,462 (30 June 2015).
Tuusula, lying on the shores of Tuusulanjärvi lake, is located in the province of Southern Finland and is part of the Uusimaa region. It covers an area of 225.46 square kilometres (87.05 sq mi) of which 5.95 km2 (2.30 sq mi) is water. The population density is 175.22 inhabitants per square kilometre (453.8/sq mi).
Tuusula has three population centres. The administrative centre is Hyrylä (about 19,500 residents), other two are Jokela (5,300 residents) and Kellokoski (4,300 residents). The remaining 4,400 residents are distributed to the rural areas outside of municipal centres.
The neighbouring communes are Vantaa to the south, Nurmijärvi to the west, Hyvinkää to the north, Mäntsälä and Järvenpää to the north east, and Sipoo and Kerava to the east.