While the quality of environmental science journalism has been the subject of much debate, a widely accepted benchmark to assess the quality of coverage of environmental topics is missing so far. Therefore, we have developed a set of defined criteria of environmental reporting. This instrument and its applicability are tested in a newly established monitoring project for the assessment of pieces on environmental issues, which refer to scientific sources and therefore can be regarded as a special field of science journalism. The quality is assessed in a kind of journalistic peer review. We describe the systematic development of criteria, which might also be a model procedure for other fields of science reporting. Furthermore, we present results from the monitoring of 50 environmental reports in German media. According to these preliminary data, the lack of context and the deficient elucidation of the evidence pose major problems in environmental reporting.