In this paper we describe our experiences in applying the concept of participatory sensing to environmental monitoring. We have run pilot trials for air quality, water quality and plant disease monitoring. In these pilots, users have reported their personal observations or measurements of various environmental phenomena, using special locationbased applications in their mobile phones. We found a relevant correlation between algae observations by untrained citizens and by professionals, which supports the feasibility of participatory sensing as a complementary information source for algae monitoring. One key issue in collecting useful participatory datasets is managing to motivate people for acting as mobile environmental sensors. Other important issues discussed in the paper include privacy preservation and reliability of user observations