OP, there are too many pieces missing to be sure. Here are some questions:
Were the birds in the water or near it?
I would assume you would not describe them as tall birds if they were swimming in the water, and you did say " next to a river."
No American bird in your region, of that size, "runs" away as you describe. Great Blue Herons take flight when alarmed but are almost always solitary and only flock in nesting colonies (in trees), which isn't how you described the birds.
Were the birds running to take flight?
Many water birds do run as they take flight. Many ducks, all swans and cormorants run on the water before taking flight.
How far away were you?
This matters in trusting your description of size and color. It also matters to whether or not the birds you heard were the ones you saw. Did they take flight because of you? Were they all calling in unison?
What was the general shape of the bird?
You give no description of the birds shape, other than tall. Was the bird tall, thin and long-legged like a heron, egret, sandhill crane? Big and bulky like a goose, swan? Long neck?
Were the birds backlit?
If so, you could not have detected the true color of the birds.
Your best clue is the sound, and only a quite large bird seen from a considerable distance has the pipes to be noticed.
Based on this clue and others I would guess one of the following:
Tundra Swan
Trumpeter Swan
Sandhill Crane
check out
https://www.allaboutbirds.org
All three of these birds hang out in flocks, have similar calls as you describe and are noticeably large.
Cormorants don't usually act the way the OP describes. They are almost always silent and this time of year don't flock together at all.