Surface waters, particularly rivers, are paramount in serving as the primary global water source and a pivotal economic driver. Various pollution sources can negatively impact water quality. The Water Framework Directive has established regulations that define specific chemical and ecological statuses for rivers. Consequently, there is an ongoing commitment to monitor their quality closely. This study involved the collection of samples from two watersheds (Laspias and Lissos) within the Eastern Macedonia and Thrace Region. The two rivers flow along regions characterized by notable environmental stressors, including WWTP, landfills, industrial zones, and agricultural areas, which also constitute substantial contributors to the local economy. This study’s outcomes, covering from springs to coast, are presented and analyzed using various indices, including the Canadian Council of Ministers of the Environment Water Quality Index (CCME-WQI), discriminate analysis, and the trophic status index (TRIX). Water quality assessment included the measurement of physicochemical parameters, common pollutants, and major ions. The analysis revealed “bad” water quality status along most of the Laspias and in specific sectors of the Lissos, with parameters exceeding the thresholds set by legislation. The rivers demonstrated significant organic and nutrient pollution. Given that water quality in these rivers is significantly influenced by urban, agricultural, and industrial runoff, the imperative need for change necessitates interventions to improve water quality. Observations and measurements are fundamental prerequisites for raising awareness among citizens and stakeholders and for finding effective management measures for the two river basins.

The Laspias River and Lissos River sustain the hydrological and ecological functioning of the Vistonida Lake wetland complex, a protected Natura 2000 site and Ramsar Convention Wetland of International Importance, by regulating nutrient transport and supporting aquatic biodiversity. Thus, the water quality of the rivers Laspias and Lissos and their adjacent coastal zones located in the prefectures of Xanthi and Rhodope (NE Greece) respectively was monitored regarding key metal concentrations for a period of two years. The monitoring of these watersheds and coastal zones was based on seven sampling stations in the Laspias River, twelve stations in the Lissos River and four stations in each river’s coastal zone. During water monitoring of both rivers, a wide range of chemical elements was analyzed to assess water quality. In the present work, the heavy metal pollution index (HPI) and the heavy metal evaluation index (HEI) were assessed in both rivers and their coastal area for four successive seasons. The mean HPI and HEI values for the Laspias River were 54.66 ± 10.82 and 1.45 ± 0.22, whereas the respective indices in the Lissos River were 14.43 ± 4.14 and 0.39 ± 0.14. The mean HPI and HEI values for the adjacent coastal zones of the Laspias and Lissos Rivers were 7.42 ± 1.52 and 0.14 ± 0.05, as well as 10.39 ± 0.83 and 0.23 ± 0.02, respectively. Therefore, the average HPI values for both rivers and their coastal zones were below the proposed threshold (<100), while the HEI of the Laspias River classified the water quality in the second category (slightly affected, HEI from 1.0 to 2.0 due to the effect of Mn) and the Lissos River in the first category (very pure/pure, HEI < 1), respectively, considering drinking water thresholds. The HEI indices of their coastal zones characterized the water quality as very pure/pure.