Hungary is rich in natural water resources, therefore investigation of these biotopes is an important task. The Szarvas- Kákafok deadarm is the largest horse-shoe lake of the Tiszántúl, its lenght is 28 km. It has an important role in recreation and agricultural utilization. The quality of the deadarm is influenced by the river Körös, but also by communal and agricultural pollution. Our goals were to estimate the intensity of the sedimentation processes, and the water- and the sediment quality as well. Also, we examined an artificial wetland system, constructed by the Fish Culture and Irrigation Research Institute, Szarvas. The calculated sedimentation was 0.4-0.5 cm year-1, which indicated an intensive eutrophication process. The constructed wetland system was able to decrease the organic load of the intensive fish culture company. On the basis of our TOC measurements, the organic matter content of the effluent water remained whitin the water quality limits. The changes of the material cycling could be more intense in the water body, then in the sediment. The oxido-reduction potential of the sediment could indicate the ecological state of the shallow lakes, therefore it could be an easily measurable indicator in the water classification.