Oh, you said that it's jarring to see them practicing without mountains and conifers in the background, so I thought the movie must have moved where they practice or something.
If I recall correctly by watching a "behind the scenes" featurette, a lot of rowing scenes were shot in the UK, so that might explain it.
Yeah, Clooney has said repeatedly that 1936 Seattle doesn't look like Seattle of today so they shot it in the UK. Whether that's a reason or an excuse, whatever. They do some far angle shots of Montlake Cut which look great except for the fact that IRL such a shot would show the Olympics in the distance. Again, it's fine, can't nitpick to the point of not enjoying it for what it is.
I just find it amusing which pieces get historical/scene precision and which ones don't. Hooverville south of downtown, with the Smith Tower in the distance, accurate per photos and the memories my dad has described to me. The Olympic 8s themselves, the ASUW shell house, some of the launch boats for the Cal race (one is named Oski III), a shout out to Hugh Laurie's dad, historically accurate. Mt Rainer, the Cascades and Olympics being absent when showing UW rowing on Lake Washington? OK. Only if you notice such things.