We have many reactors in the US that sit on the great lakes and the ocean, both of which don’t suffer this problem.

No, you just don't have environmental regulations in the US.

The reason those plants have been shut down wasn't because they can't technically operate in the summer heat (as any thermal power plant, they do operate on a temperature difference, so warmer cooling water will lower their efficiency, though), but because the temperature of the cooling water released would be high enough to endanger the ecosystem in the body of water they draw their cooling water from.