FILUM AQUAE. The thread or middle of a water course. (q.v.)
2. It is a general rule, that in grants of lands bounded on rivers and
streams above tide water, unless otherwise expressed, the grant extends
usque ad filum aquae, and that not only the banks, but the bed of the river,
and the islands therein, together with exclusive right of fishing, pass to
the grantee. 5 Wend. 423.