At what percentage of impervious cover do streams start to experience significant impacts?

Streams begin to experience significant impacts when impervious cover reaches around 25%. This threshold is critical because impervious surfaces, such as roads and buildings, prevent rainwater from being absorbed into the ground, leading to an increase in stormwater runoff. When impervious cover exceeds 25%, the volume and velocity of runoff increase, causing erosion, sedimentation, and pollution in nearby water bodies. This level of development can disrupt the natural hydrology, degrade water quality, and negatively affect aquatic habitats and biodiversity. Understanding this percentage is essential for stormwater management and for establishing policies to protect water resources and maintain watershed health.