Urban estuary serves as a critical nexus for the land-sea transfer of the terrestrial pathogen Toxoplasma gondii.

Terrestrial runoff is a key pathway for the transmission of the terrestrial pathogen Toxoplasma gondii from land to sea, posing a significant threat to marine ecosystems. Understanding the mechanisms by which T. gondii is transported from terrestrial to marine environment is crucial for developing effective prevention and control strategies for toxoplasmosis in marine organisms. This study investigates the transport of T. gondii through terrestrial runoff in the Sow River, a representative watershed in Weihai, China. Surface water, bottom water and sediment samples were collected and analyzed for T. gondii DNA using PCR methods. Out of 5328 samples, the prevalence of T. gondii was found to be 8.61 % in surface water, 9.80 % in bottom water and 16.61 % in sediment, with sediment identified as a significant reservoir. Additionally, estuarine zones showed a higher prevalence of T. gondii (16.80 %) compared to riverine areas (9.00 %). The study further revealed that seasonal climate variations, such as temperature and precipitation, had no significant impact on the distribution of T. gondii. However, there was significant spatial variability, with estuarine conditions facilitating increased pathogen transmission. These findings highlight the importance of estuaries and sediments as key conduits for T. gondii entry in marine food webs. The results provide a theoretical basis for designing infection prevention and control strategies aimed at protecting marine ecosystems.