Zimar stream has become since the 1950's a sewage drain. stream extends over 27 km from the west of Nablus City to Tulkarem City northwest of West Bank. are lost opportunities for streams' water bene use, and nature conservation principals have been severely violated for the Zimar watershed, in addition to public health and biodiversity threats. paper was prepared to predict the water quality of the Zimar's stream under current and proposed future conditions, and under di scenarios. Dissolved Oxygen was taken as the main quality parameter, and depending on steady state solutions of Streeter-Phelp's equation. QUAL2Kw model was used to predict the behavior of the stream. Water samples were collected, and measurements were conducted for eight di critical locations along the stream, and during the wet and dry seasons of 2011–2012. Several scenarios were simulated, taking in consideration the in of the under-construction wastewater treatment plant in the western area of Nablus city, proposing additional wastewater treatment plant at Anabta village, and proposing constructing of three arti weirs. It was found that the stream has signi self-puri capacity as the dissolved oxygen concentration doubled from Nablus city to Anabta village; midway to Tulkarem. Biological oxygen demand between those two points decreased to values up to 11% from the original value. paper supports proposed solutions of the stream to improve its water quality, and enhance aesthetic views in the catchment.