Koskenkylänjoki ("river of rapid village" literally) or Pernajanjoki starts at Pyhäjärvi
in Southern Finland
. It runs trough municipalities of Lapinjärvi
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)