A survey of Oncomelania quadrasi was conducted from December 2012 to February 2013 in the Municipalities of Kapatagan and Lala, Province of Lanao del Norte, Philippines to geo-reference location of snail colony sites, estimate snail population density and its environmental determinants, and determines the prevalence of S. japonicum-infected snails. Out of 29 total villages surveyed, 25 (86.21%) were positive of infected snails. 104 (58%) of 180 water body sites (canals, streams, springs, swampy areas and wet grasslands) inspected had O. quadrasi snail colonies. Population density averages 9.9 } 8.1SD to 11.7 } 6.9SD snails per colony. Multivariate canonical correspondence analysis revealed that a combination of large habitat size of 1000-3000 sq km (p < 0.002), 0-11 cm water depth (p < 0.002) and 30.7-32.8 oC water temperature (p < 0.006) significantly explained high density of O. quadrasi populations. The mean prevalence of infected snails was 1.4 } 0.8SD and 1.1 } 0.3SD per colony in Kapatagan and Lala, respectively. The prevalence of S. japonicum infection in O. quadrasi is low but indicates active transmission. The geographic position of the irrigation system seems to promote the spread of O. quadrasi in the vast network of water bodies. Hence, multi-factorial and intensive control measures are necessary to prevent transmission of schistosoma infection.