Farming practices and other anthropogenic influences have affected the water quality and shifted trophic state of Lake Trichonis, western Greece, from oligotrophic to oligo-mesotrophic. This change has been accompanied by an expansion of dense reed beds ofPhragmites australisin places where limited growth existed in the past. This study measured the seasonal changes in nutrients and heavy metals in the reed beds of Lake Trichonis, and assessed the applicability of reed harvesting on maintaining or improving the water quality of the lake. The results have illustrated three types of accumulation dynamics of nutrients and heavy metals in the reeds of Lake Trichonis. The first type shows maximum accumulation occurring early in the growing season and gradually declining throughout the year. P, K, Cl and NO3follow this type of accumulation. The second pattern followed by fluoride, showed constant accumulation throughout die year. The third accumulation pattern, followed by Na, Zn, Cd, Co, Mn, Fe, Mg, Ca, Cu, Al, Ni, Cr, and SO4, showed increases in accumulation throught the growing season, reaching a maximum in August and September and then declined steadily. The reeds beds are a significant sink for nutrients in the early growing season and a potentially significant source of nutrients later in the season. The results indicate that removal of the reeds in the early spring would remove a large reservoir of potentially mineralizable P from the lake. To properly control the flow of nutrients and heavy metals in a lake through reed harvesting, the dynamic cycling of P and die seasonal changes in accumulation should be considered.