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The Tonle Sap ecosystem of Cambodia is situated in the lower part of the Mekong River basin (MRB), the TS ecosystem water environment is influenced by 181,035 km 2 of its catchments and water inflow from 4000 km in length of the upper Mekong River. The water quality index (WQI) was developed based on seven environmental chemical factors of DO, NO 3 +NH 4 , TOTP, TSS, temperature, pH and conductivity at Kampong Luong monitoring station during the period 1995 -2002. On PCA, among 15 candidate parameters, the six most variation parameters of 'concentration of TSS mg l -1' , 'temperature C degree', 'conductivity mS m -1 ', 'ratio between N and P', 'average monthly variation of NO 3 +NH 4 N', 'average monthly variation of pH', were identified and selected to constitute the WQI. Each parameter was scored as 1, 3 and 5 and narrated, in order, as poor, fair and good conditions. The yearly WQI score was calculated from these six parameter scores in the relative year. The WQI showed that the highest score of 4.3 was in 1996, while the lowest scores were of 1.3 and 1.0 in 2002 and 1998. Importantly, the WQI was significantly (P<0.05) correlated with the 'dai' fish catch (r 2 = 0.858) and the fish biological group 4 (r-species) (r 2 = 0.75) during the period 1995-2002 indicating that the index was sensitive to reflect the relation between water quality condition and fish production. Then the WQI should be considerably used as the biological monitoring tool for water quality -fish production assessment. The correlations (P<0.05) between WQI and fish families of Gyrinocheilidae and Cyprinidae indicated these fish families should be considered to be used as the TS ecosystem water quality bioindicators. Keywords: Tonle Sap ecosystem, water quality index, 'dai' fish catch, fish biological group, k and r strategy species and multi-parameters analysis.

Riverbanks are an important source of plastic pollution. However, the current assessment methods for riverbank litter are based on a point-based sampling which is time consuming and limited in scope. To quickly assess hotspot areas and litter compositions in larger areas, this study developed a new citizen science bicycle survey for riverine debris. Covering 281.5 km of the Tamsui river system in Taiwan, the new methodology was tested at one of the most plastics polluted rivers in the world. The results revealed an average litter density of 15.3 m3/km at the river mouth and of 0.2 m3/km to 2.8 m3/km along the riverbanks further upstream. The coastline was mainly polluted by derelict fishing gear whereas single-use plastics and illegally dumped waste dominated the upstream areas. A correlation between litter and population density could not be identified, but it was noted that litter hotspots occur at cut banks and near mangrove vegetation. Overall, the new methodology proved suitable to collect large quantities of data for scientific purposes and to quickly detect litter accumulations prior to clean-up activities.