This slide presentation outlines the identification and resolution of a distribution system water quality event for discolored or yellowed tap water in New Jersey's Monmouth County. Numerous flushings were performed and one sample at an interconnection was yellow and contained >2 mg/L manganese but low iron. However, combined filter effluent samples collected every 4 hours showed low (<0.04 mg/L) Mn levels. The local treatment plant practices included: water is ozonated, coagulated with PACl, and then split to six purification Units (upflow sludge blanket clarifier/filters); chlorine, fluoride, zinc orthophosphate, and caustic are added before water enters clearwell; ozone added at 2-3 mg/L; no residual leaves the contact basin; and, finished water at pH 7.5 and 1 mg/L orthophosphate. The investigation is outlined as follows: examined plant records for raw, filtered, and CFE for turbidity, TOC, iron and manganese; examined distribution system sample records for color, orthophosphate, iron, manganese and HPC; and, collected sludge blanket samples, found low levels of manganese in interstitial water but when samples were digested in hydrochloric acid, manganese levels were greater than 10 mg/L. The hypothesis included: increase in water temperature and algae combined with preozonation resulted in increase biodegradable organic carbon in sludge blankets; blanket(s) became anoxic leading to manganese release for a short period of time (several hours at most); and, dissolved manganese passed through filters and reacted with post-filter chlorine and slowly precipitated causing yellow water. The resolution included: plant had been upgraded to discontinue prefilter chlorination to avoid making disinfection byproducts (DBPs) so plant staff wanted to discontinue chlorination; preliminary tests showed that the granular activated carbon (GAC) filters could remove at least 0.5 mg/L permanganate; and, began sodium permanganate feed, increasing level until pink water was observed above filters. Includes figures.