For much of the year, the Outer Mackenzie Delta is encased in sea ice and its numerous rivers, channels and lakes are covered by freshwater ice. Increased sunlight, warmer spring temperatures and the arrival of warm melt water from the upstream Mackenzie Valley trigger the melt and the eventual breakup of ice in the delta. RADARSAT-1's sensitivity to different types of ice and its ability to acquire imagery regardless of cloud cover makes it a useful tool to monitor this short-lived annual event. In this June 1, 1997 image(right), the sea ice barrier (A) that prevents the Mackenzie's spring discharge waters (B) from entering the Beaufort Sea (C) is clearly visible. Individual floes (D) are easy to find on the seaward side of this thick ice barrier. Brighter areas indicate ridged ice areas, while dark, homogeneous textures represent smoother ice surfaces. Channel ice (E) is visible within the main channels of the delta. With a dry snow cover, smooth lake ice (F) appears dark as the radar penetrates the homogeneous ice volume and is absorbed by the lake bottom. Dark areas on the active delta (G) indicate overland flooding caused by the large annual increase in upstream discharge and snowmelt in the outer delta.