The depth of the Columbia River varies significantly depending on the location:

• In urban areas and most parts near cities like Portland, the river is generally around 20 to 40 feet deep, with some points near Portland reaching up to about 75 feet.
• The deepest parts of the river are often in reservoirs formed by dams, with depths exceeding 350 feet. For example, Franklin D. Roosevelt Lake, a reservoir on the Columbia, reaches depths around 350 feet.
• The natural river depth away from dams and urban areas typically ranges between 25 and 45 feet.
• The Columbia River Gorge itself is a very deep canyon, up to 4,000 feet deep, but the water in the gorge is comparatively shallow, with the deepest parts around 90 feet.
• Historical flood events, such as the Missoula Floods, temporarily increased water depths dramatically, with estimates of up to 400 feet near modern Portland and as deep as 1,000 feet at locations like Wallula Gap, though these are not normal conditions but exceptional flood-related depths.

In summary, under normal conditions, the Columbia River depth is usually between 20 and 75 feet in many populated areas, but it can reach depths of over 350 feet in dam reservoirs and possibly even deeper during historic flood events or in certain natural deep spots.