This is research for a book I am writing and I strongly suspect the answer is no, however I can not quite get Google to spit out a direct answer. :-)

If you have a lake, attached directly to the ocean via a large river, would the water level in that lake rise and fall with the ocean tides?

From what I can find, lakes in general do not have meaningful tides, but I can find no clear answer on how a lake attached to the ocean would act. Or... I am not asking Google the right question. :-)

The set up I am imagining is a large lake that empties into a 8 mile or so river. That river, in turn, empties into a large bay, like New York Harbor, or the Delaware bay.

I figure one of three things will happen as tides come and go:

  1. Nothing. :-)

  2. The water level and in both the river and the lake will drop relative to the ocean level dropping/receding as water seeks it's own level.

  3. The water level and in both the river and the lake will drop in some manner, but will be negligible by the time it reaches the lake.

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    $\begingroup$ Ocean tides are standing waves that the moon and sun excite in Earth's large ocean basins. Lakes just aren't big enough for standing waves of such long periods, and the river connecting the lake to the ocean is too small to let any of the wave energy through. m.youtube.com/watch?v=PSJRymZ5bJs $\endgroup$ Sep 28, 2023 at 0:59

1 Answer 1


Most lakes are are unaffected by ocean tides, but tidal lakes do exist.

Most tidal lakes have a short connection to the ocean, with salt water flowing in and out with tides, making the lake's water salty or brackish. A good example is Nitinat Lake on Vancouver Island that is a mostly salt-water tidal lake with a fresh-water layer on top, connected to the ocean via a 3 km long narrows. Tides drive tidal bores up the narrows into the lake.

In a few cases, however, ocean tides raise the fresh water level in a river which in turn changes the level in a fresh-water lake:

To get such fresh-water tidal lakes, you need a river whose water level is raised and lowered near its mouth by ocean tides but whose flow is large enough to prevent salt water from penetrating upstream. If the river's gradient is shallow enough, tides can affect the river's level for many kilometers upstream from the ocean. If a fresh-water lake is connected to the river, its level may also rise and fall with the tides.


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