A geomorphic assessment was conducted on the two branches of the Upper Morningside Tributary, located in Markham, Ontario. The morphology of each branch is influenced by urban development; on the North Branch a large stormwater detention pond has further altered conditions. Based on site observations, the current channel condition in the North Branch is characterized as morphologically inactive, while the West Branch is actively unstable. The lack of channel adjustment in the North Branch is attributed to the subdued discharge regime and the lack of sediment supply associated with the detention pond. The channel is characterized as 'sensitive' to change in the prevailing hydrologic condition, based on the boundary material erodibility and 'sediment starved' nature of the reach. Based on the findings of an erosion simulation study, the North Branch is expected to become morphologically unstable with a ten percent increase in the basin imperviousness, despite the detention storage provided by the pond.