Our study investigated the feasibility of using a constructed wetland for restoring a creek that had been seriously polluted by organic discharges from animal husbandry activities in the watershed. A fish-ladder type cascade was used to raise the average dissolved oxygen (DO) from 1.0 to 3.6 mg/L. The ecological treatment system removed 64.0% of suspended solids (SS), 43.0% of biochemical oxygen demand (BOD), and 11.0% of ammonia nitrogen. Additionally, reductions of BOD and nitrogenous biochemical oxygen demand (NBOD) were simulated using a first-order biokinetic model for biodegradation of organic matter. The monitored data fell within ranges of the model-based BOD and NBOD reductions, although NBOD reduction was over predicted. Hence, the first-order biokinetic model appears useful for estimating BOD and NBOD reductions in a constructed wetland.