Koskenkylänjoki ("river of rapid village" literally) or Pernajanjoki starts at
Pyhäjärvi of
Porlammi in
Southern Finland. It runs trough municipalities of
Lapinjärvi,
Liljendal and
Pernaja where it runs to
Baltic Sea.
It's length is 38 km and it gathers water from area of 895 km^2.
Volume of water in the river varies from 5 m^3/s (february) to over 20 m^3/s (april)