It only becomes a visible problem in harbours (or otherwise in shallow waters).
It looks like a tidal wave in the sense that it's a lot of water moving in a given direction. The mechanism causing it is not the same at all, so the name tidal wave is misleading.
As an example a friend of mine was on a boat during the massive 2004 tsunami, but since he was a few miles off the coast where the water was deep he didn't even notice the tsunami sweeping under his boat. Once it hit land it did massive damage.
It's because the tsunami only becomes visible when it hits your harbors. They used to be called "tidal waves," but the term is inaccurate — that's why it isn't used anymore. They're not like normal waves out at sea, and they have nothing to do with the tides. The fact that it "looks like a big surge side rolling" in does not actually make it tidal.
