Abstract. The ecological damage to the environment through fish farming could be reduced by using wheat straw mattress for filtration the sewage. Dryness, nitrogen and phosphorus impact by means of sewage from intensive fish farming could be reduced about 50%. The chemical need of oxygen requirement which causes the sewage fee could be reduced about 20% that means there are likewise economic advantages if straw filter is used. In addition the remain left over the filter and the straw which built up the compost could be used for plant production. The similar structure and small costs make a possibility to use straw filter in small fish farms for reducing environmental impacts.