I have found and enjoyed some interesting routes based on a low water crossing of the River Avon at Bantham in Devon. The crossing is about 1/4 mile upstream from the ferry which never seems to operate. In summer it is rarely deeper than knee deep usually a lot less and with a sandy bed easy to walk in bare feet.
Just a matter of adjusting your route to time with the tide tables. Yet to try a crossing of the River Erme at Erme mouth, though there is a ford upriver, not marked on OS, rather stony bottom. Incidentally there is no righteous way to This feature of our countrysides geography, there is a footbridge, did have locked gates but Mrs BWW was quite capable of following my excursion around this trifling impediment.