Find out the hidden depths of the Columbia River in Washington and Oregon

The Columbia River runs through Tri-Cities - and many other communities in Washington and Oregon. We cross it for work, walk along it, play in it, fish in it - and it plays a key part of the Pacific Northwest region's ecology and economy. But because we live alongside the river daily, sometimes we take it for granted. So, pop quiz time:

Just how deep is the Columbia River?

Without Googling, the odds are, you don't know. You might remember that the Congo is claimed to be the deepest river in the world at 600 feet. So what's a good estimate from there - half that at 300 feet? A quarter, at 150 feet?

It turns out the answer isn't quite so obvious - but I've done a deep dive to uncover the truth.

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The challenge: river depth varies by location - and time.

Location affects river depth - that much makes sense. Of course rivers aren't like paved highways along the bottom; they rise and fall based on the landscape around them and the history of the land before them (such as the Missoula Floods that helped generate our local geography). There will be low points and high points, and measuring them requires scientists running river gages to determine the river depth.

However, river depth also varies over time. The image below shows the depth measurement at the Dalles in Oregon on the Columbia over the past year - which has ranged from about 73 to 79 feet (putting it at a mean value of 76 feet).

Of course, this is a small span of time when it comes to rivers, which exist for millennia and can be affected anywhere along their path by seasons, natural disasters, climate change, and human efforts like dams and bridges.

A closer look at Columbia River's depths

Because location and time lead to so much variance - and we haven't installed gages throughout the river path - it's hard to know exactly how deep the Columbia River truly is at its deepest point. Some information online can be accidentally misleading, as it may reflect historical river depth versus active river depth.

A Reddit user actually goes into depth on the science of why river depth is hard to measure. Their explanation led me into finding a useful way to estimate the depth of the Columbia River.

Using nautical charts, which utilize a variety of methods to collect data about the river bed, we can get an estimate of the river depth at any specific point along the Columbia River. Thanks to a map put together by Fishermap.org, I've looked to find out some of the interesting depths along Washington and Oregon's portion of the Columbia River.

How deep is Columbia River Gorge?

Despite how deep the landscape is in the Columbia River Gorge near Mt. Hood, the water is actually comparatively shallow. The deepest parts are on the west end of the Gorge and only reach around 90 feet. Most of the water, even at the widest part of the river, is only 25-45 feet deep.

How deep is the water near Portland, Oregon?

Most of the river that runs through Portland is 20-40 feet deep. A few points northwest of Hayden Island drop up to 75 feet.

Overall, where is the Columbia River the deepest?

As noted above, dams create unnaturally deep river levels, and so many of our deep waters are near large dams and reservoirs. From my scouting along nautical maps, it looks like - at least in the United States - the Franklin D. Roosevelt Lake is the deepest part of the Columbia River at around 350 feet.

However, many of the cities built around the river - like Wenatchee, Tri-Cities, and Portland - are in relatively shallow areas of the river where depths rarely go farther than 50 feet. Why is that? Well, a lot of it likely has to do with bridges: the deeper the river, the harder it is to build and secure a bridge crossing.

So the next time you look out at the Columbia River - give a little moment of your time to appreciate its secret depths, and what is hidden beneath that we still don't know.