A resin cultivating base serves as seedling beds for vegetation which are planted and are partially immersed in a river, lake, marsh, pond or waterway. The resin cultivating base is a three-dimensional structure constituted by long and short filaments of thermoplastic resin. The long and short filaments are curled or looped at random, and contacted, entwined and gathered, thereby forming a low density portion and a high density portion. Vegetables planted on the low density portion of the resin cultivating base suck nutritious salt such as phosphor and nitride. Microorganisms living in the resin cultivating base decompose organisms in the water, thereby purifying the water. <IMAGE>
