When fly fishing in montana
you have the right to move up and down a stream if you are within the high water mark. On O'dell spring creek the high water mark is basically the existing water level since it doesn't fluctuate much so you have to stay in the creek. As long as you access it from a public spot like the bridge outside of Ennis you can wade upstream as far as you want. The stream access law also allows you to move outside of the high water mark to navigate around obstacles like fences.