Based on a rational and simple chemical approach, a field-investigation aimed to assess the role played by a natural channel "lama" on the quality of underlying groundwater and neighbouring soils has been carried out. The results have demonstrated that: (a) the stream flowing through the "lama" is mainly made up of treated effluent from a nearby municipal wastewater treatment plant; (b) the occurrence of nitrates in the "lama" is due to rain-washing of nitrogen fertilized agricultural soils bordering on the "lama"; (c) hydraulic connections exist between the lama and the underlying groundwater causing contaminants flowing through the "lama" to reach groundwater within less than one week; (d) compared with the values measured in the "lama", the concentrations of TOC, N-NH4 and N-NO3 in groundwater result: lower, far lower and greater, respectively; (e) agricultural soils bordering on the "lama" result significantly contaminated by halogenated organics.