Valkjärvi is a lake located in the Nurmijärvi municipality in Southern Finland.

It is an island-free lake in the immediate vicinity of Klaukkala's urban area.

[1] Valkjärvi is the most lushest lake of Nurmijärvi,[2][3] and it is part of the Nurmijärvi's lake monitoring program of the Central Uusimaa Environment Centre (Keski-Uudenmaan ympäristökeskus) due to its poor oxygen values near the bottom of the lake, which are observed especially in summer and winter under ice.

[4][5] Blue-green algae are quite common in the lake; in July 2015, the phytoplankton in the lake with the highest total biomass consisted of 40% cyanobacteria and 29% cryptomonad.

[2] Despite all this, Valkjärvi has great recreational value and there are quite a lot of both permanent and holiday settlements around the lake.