Sound knowledge of the local distribution and diversity of freshwater snail intermediate hosts and the factors driving the occurrence and abundance of them is crucial to understanding snail-borne parasitic disease transmission and to setting up effective interventions in endemic areas. In this study, we investigated the freshwater snails, water quality parameters, physical characteristics of habitats, predators and competitors, and human activity variables at 102 sites during December 2018 and August 2019 in Shenzhen and adjacent areas in China. We used decision tree models and canonical correspondence analysis to identify the main environmental and biotic factors affecting the occurrence and abundance of snail species. A total of nine species of snail were collected throughout the study area, with Biomphalaria straminea, Sinotaia quadrata, and Physella acuta being the most predominant species. Our study showed that the most important variables affecting the abundance and occurrence of snail species were the presence of predators and competitors, macrophyte cover, chlorophyll-a, substrate type, river depth, and water velocity. In terms of human activities, snail species occurred more frequently and in larger numbers in water bodies affected by human disturbances, especially for sewage discharge, which may reduce the occurrence and abundance of snail predators and competitors. These findings suggest that proper management of water bodies to reduce water pollution may increase the abundance of snail predators and competitors, and should be considered in integrated snail control strategies in the study area.

[Background]Schistosomiasis mansoni is one of the most prevalent neglected tropical diseases transmitted by snails of the genus Biomphalaria . The pla norbid freshwater snail Biomphalaria straminea as an invasive vector is expanding its geographic range for its great dispersal capacity in Gonuangdong Province, causing potential risk of an epidemic of S. mansoni in southern China . Previous studies have mainly focus ed on the environmental factors that affect B straminea’ s distribution, but few studies have looked at its hydraulic characteristics for the water conservancy control. This stud y explored its primary parameters of the hydraulics characteristic s including density, hydrostatic setting velocity and l ocomotion in different water depth to evaluate its peculiar dispersion characteristics in natural environment. [Methods] The density and hydrostatic setting velocity of B. stramine were measured by the drainage volume method and setting tube method, respectively. T he behavior and distribution characteristics of B. stramine in different water depths were observed by the Plexiglas tube method and the effect s of hydrostatic pressure on the climbing speed of B. stramine were also analyzed. [Results] Our results show that the average density of the B. stramine is 1.08 g/cm 3 . The hydrostatic setting velocity of B. stramine is between 2.32 cm/s and 12.92 cm/s in the water , there is no significant difference betwe en the settling velocity and their shape type. In the Plexiglas tubes with different depths, we noted that the locomotion can occur in six manners. The B. stramine distribute mainly along the surface and at the bottom layer of the tubes and the proportion of the B. stramine on the surface water generally raised as time increase d. Also, we observed the climbing speed of B. stramine at different water depth, and obtained the regression equation of the hydrostatic pressure and their climbing speed of the B. stramine . It revealed that the climbing speed of B. stramine increases first and then decreases with the water depth increase, and reaches the maximum when the water depth at 120cm. [Conclusion] The findings of this study indicate that there are si gnificant differen ces between the 50 density , the hydrostatic setting velocity and climbing speed of B. stramine compared with 51 Oncomelania hupensis . Future studies should be conducted more intensive on h ydraulics 52 characteristics of B . straminea and thus establish adequ ate water conservancy measures to control 53 its dispersion