Several years ago, Marjorie and I and Taylor (our pooch) decided to canoe the Duwamish River in Seattle. Our plan was to put in just above the sort of confluence with the Black River; I use sort of because what’s left of the Black River is the merest remnant of what was the former outlet river of Lake Washington. We would then float about 11 miles down to the mouth of the Duwamish at Elliott Bay. As experienced canoeists from Utah (Taylor included), we thought the trip would take a couple of hours, taking advantage of the gentle current. We were having a dandy time, aided by a downstream wind, until about mile 5, near some Boeing buildings, when paddling became much harder. It felt like we were now going the opposite direction—upstream against the current. Perhaps, we thought, we were bonking, not having eaten much, but then we came to a startling and never-before-encountered canoeing experience. We were paddling upstream, not against the river current but against the Pacific Ocean and the incoming tide, a phenomenon not felt in our Utah-canoeing careers. Who would ever think of tides on a river? Clearly, we hadn’t. Suffice it to say, with our tails between our legs (though Taylor didn’t cotton to such behavior), we abandoned the trip and headed home but not before a wee bit of an epic getting back to the put in. (That’s another story.) I am regularly reminded of this experience, primarily because friends of ours annually put together a river trip on the Skagit River. Each August, when the weather is fine and the timing is right, the trip begins a few miles from the mouth of the river. We paddle down river with the current to a massive sandbar, where we pull the boats up on the sand, establish a base of fun (eating, sitting, strolling, swimming, etc.), and hang out until we get to embody a cliche—a rising tide lifts all boats. (Apparently, this aphorism relates to the economy but being literal and more nature focused, I prefer to stick to its true meaning.) (Above is a 53-second video of the advancing tide.) This is one my favorite times on the sandbar: watching as the tidal advance moves toward us. At first, it seems far away, barely inching forward, but then you look again and you realize, wow, the front is hauling tuchas in our direction. As the tide floods in, everyone gets in their boats, waits patiently until they float (which is not quick with four people and a dog), and heads out into the river. Aided by the incoming Pacific Ocean, we then paddle the couple of miles back to our put in. (This reminds me of the legendary Utah river trip question of “Do we end the trip where we started?” No we don’t…unless you’re on the Skagit!) Truly a delightful day! Our recent adventure got me thinking about tides in Puget Sound and wondering which river has the greatest tidal influence. By this, I mean, on which river do tidal waters travel farthest upriver. Figuring this would be pretty easy to find out, I reached out to several potamologists I know. Reader, I was wrong. No one tracks such fascinating information; it would require setting up numerous gauges along rivers, which costs too much money and doesn’t really aid those who focus on riparian issues. My river-focused colleagues told me that how far a flood tide travels depends primarily on the gradient of the lower stretch of the river. The shallower the gradient the greater the incoming water propagates upriver. Not surprisingly, geology dictates the gradient. In Puget Sound, lower gradient rivers, such as the Snohomish, Snoqualmie, Duwamish, and Sammamish, were carved during the last Ice Age beneath the Puget lobe glacier. In contrast, higher gradient rivers (on average 10x steeper), such as the Stillaguamish, Nisqually, and Deschutes, formed post-glaciation as rivers draining the Cascades cut into the Ice Age sediments. In other words, the tidal influence should tend to be greatest on rivers in the glacial valleys (low gradient) and less in the post-glacial valleys. River gradient is not only the primary factor influencing the tidal/river interface, but also the most fixed, at least relative to the human time scale. Far more mutable are downstream flow, tidal magnitude, wind, and atmospheric pressure. For example, winter tends to have the highest tides, but winter river discharge rates tend to be higher, too, which prevents upstream propagation. In contrast, a lower high tide in summer might travel farther because of less flow in the river. Also on a human time scale is development. Dredging, straightening, and wetland alteration have all altered river discharge and tidal advance, as have dikes, tide gates, and levees. In other words, how tides influence Puget Sound rivers is complicated, incredibly dynamic, and always variable. Consider the river where I first encountered the protean world of tide vs river, the Duwamish. Below are two graphs illustrating the variation caused by tides. Looking at the graph, I realize that Marjorie, Taylor, and I had been on tidally-influence waters the entire time we floated the Duwamish. We had been fortunate to have spent part of our river trip on an ebbing, or slack, tide and not the entire time battling the flood tide. Two things stand out about these graphs. On the upper one, you can see the trouble we faced on our canoe trip—during flood stage the discharge is negative, meaning the entire river is basically defying the most obvious effects of gravity (e.g. water flows downhill) and headed backwards. The second is simply how the river changes so dramatically with the tides; it’s a beautiful manifestation of how water is the life blood of the planet, pulsing rhythmically with the twice-daily interactions of the moon, sun, and Earth. As I have written before (Tethers of Tide and Time and Tide), most of us (and I recognize that I am one of us) overlook or ignore this astounding feat and feature of the natural world. I get this tidal blindness. We don’t have to think about the tide; it has little apparent effect on our daily lives, except perhaps with an unusually high or low one. Yet, tides are arguably one of the planet’s great natural history events, and for those who live in Seattle or near a coast, they are also one of the easiest to see and to experience. So, go on, get outside and watch the wonderful changing of the water but make sure you look at a tide chart ere you do. Word of the Week - Potamologist - One who studies rivers, from Greek potamos (river). A printer named George Smithfield appears to be the person who coined this splendid word in 1829, though potamus has been plying its way through English for centuries. Consider such words as Mesopotamia (between two rivers) and hippopotamus (river horse). Still Time to Register September 19, 2025 - HistoryLunch - HistoryLink - I have long been a fan and supporter of this fine organization. If you are not aware of it, the website is the site for history about Washington state, often bringing to light overlooked, under appreciated, and forgotten but vital stories. HistoryLunch is their annual fund raising event and I am honored to be the keynote speaker this year. The event is titled Is the Mountain Out? So if you want to support a worthy cause, come on by. Here’s the registration link. September 20, 2025 - Clima Incognita: Planning For An Unknown Climate – Jaipur Literature Festival: Seattle – Town Hall – 12:00 PM – 12:45 PM – I will be in conversation with author John Vaillant (Fire Weather, a brilliant book) and Brinda Sarathy (professor and Dean of the University of Washington: Bothell School of Interdisciplinary Arts and Sciences). Should be fun and interesting, along with the rest of the festival. Get full access to Street Smart Naturalist: Explorations of the Urban Kind at streetsmartnaturalist.substack.com/subscribe