The nutrient load introduced into flooded rice fields is one of the main factorsthat impact this type of ecosystem, contributing to the development of bloomsof pigmented euglenoids. This study was carried out to investigate thebehavior of red euglenas, a group of pigmented euglenoids, forming blooms inthis type of environment. Sedimented spores in the soil after water drainage,as well as water samples from vegetative cells in living blooms were collected.The collected material was inoculated into a culturing medium for microalgaeand incubated for three weeks. The cultures grown in nutrient medium wereused for morphometric analysis to identify the species. In order to characterizethe water environment, chemical and physical parameters were alsomonitored "in situ". The results indicated Euglena sanguinea Ehr. as thebloom-forming species and nitrogen as a key element in the behavior of thisspecies in this type of ecosystem. It was suggested, however, that more studiesare needed to indicate the use of red euglenas as biomarkers of nitrogenoverload in flooded rice fields
