These are the steps you may take for the purpose of solving the problem:
1. photograph the event if possible;
2. Write a brief statement about the event and describe as precisely as possible how to arrive to the location (if there is a correct address, some visible object, distinctive sign and the like.)
3.Send a statement together with your photo to the environmental inspection (okolis.inspekcija@mzoip.hr) or in writing to the Ministry of Environment and Nature Protection: Radnička cesta 80, 10 000 Zagreb, or via the telephone number 01/3717-111, contact the police (192) or the fire department (193), or municipal services monitoring officer in your city, town, or municipality.

WHOM TO CALL: and/or Green Phone service for your county (072 123 456) - the report may be sent anonymously, too.
NOTE: You can always call the service 112, especially if it is a matter of great urgency, and during the weekends, holidays or at night