Tides in lakes attached to the ocean

Question

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.

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:

• Perhaps the best known and possibly largest fresh-water tidal lake is Pitt Lake in British Columbia. Ocean tides drive water back up the Fraser River into the Pitt River and then finally into the lake which is about 50 km upstream from the ocean but only a few metres above mean sea level. The salt water doesn't make it to the Pitt River or Lake, but causes the fresh water in the river to vary by about two metres, which in turn causes one metre tides in the lake.

• A smaller fresh-water tidal lake is Lake Waihola in the far south of New Zealand. Unlike the very deep Pitt Lake (max depth 143 m), Waihola is very shallow with an average depth of only about 60 cm at low tide, and just over a metre at high tide. Ocean tides drive water back up the Taieri River into the very short Waihola River and then finally into the lake which is about 15 km upstream from the ocean.

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.