To get a Lv.173 Wartortle go to Cinnabar island an surf up and down nearest to the shore. It may take a minute but a wartortle will show, if you picked a sqirtle at the begging of the game this is pretty much useless, to capture this tought pokemon put your best at the top and pound him until 10% of his life is dead then use ultraballs and you should catch him. Note: If he gains any exp. points he will move to Lv.100.