Enchorchment of public place

Sir, in my area many years back an earth dam was built to control the floods from river. but now some of the people are occupied on and one side of the earth dam Built houses on permant basis. Government has not taken any action up to now beacuse of political pressure. How can it expose in llegal mannaer to court as well as government. Kindly give the information with respect to acts and pervious examples.