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Background: Combined sewer systems (CSS) are used by over 750 cities in the United States. They collect storm and sewer water into the same pipes for transport to a wastewater treatment plant. Combined sewer overflows (CSOs) occur during large storm events, when increased volume and flowrate of stormwater runoff cause CSS pipes to exceed capacity. Waterbodies affected by CSOs are organically rich and lack enough oxygen for larger organisms to survive, making them favorable breeding environments for mosquitoes. Stormwater control measures (SCMs), also commonly known as best management practices, utilize retention, infiltration, and/or phytoremediation techniques to decrease the flow rate and volume of stormwater runoff that flows into CSS pipes, thereby decreasing CSOs. Methods: We are researching whether SCM located within a sub-sewershed can decrease the number of mosquitoes surrounding the respective CSO outfall. Mosquitoes caught in our study site, Washington DC, included 850 in the genus Aedes, known to spread Chikungunya, Dengue Fever, West Nile, Yellow Fever, and Zika, and 1,159 in the Genus Culex, known to spread encephalitis and West Nile. Preliminary Results: Based on preliminary results, sub-sewersheds that have a higher density of SCMs have fewer Aedes and Culex mosquitoes at the respective CSO outfalls. SCMs in the sub-sewersheds may have a larger impact on Culex than Aedes mosquitoes, possibly because of a reduction in Culex mosquitoes’ preferred breeding environment, waters containing high amounts of organic matter. Though SCMs may decrease mosquitoes at the CSO outfall, we also studied whether pooling utilized by SCMs contributes to the number of surrounding mosquitoes. Conclusion: Findings from this study may help inform cities of the benefits and drawbacks of using SCMs including decreasing the vectors of mosquito borne diseases in areas with CSOs.