Simulium penobscotensisSnoddy and Bauer preferentially colonized vegetation of the generaPotamogetonandSparganumat water velocities ≥ 0.30 m/sec. ThePotamogetonandSparganumvegetation was primarily in water<1.25 m in depth, and in beds with 50–100% vegetation cover. There was an 80% increase in potential habitat of this description when Penobscot River water levels increased by 40 cm.