I would fish at night and approach from above on the opposite, right side of the bank.

I would use a Borger collared leech or a Kelly Galloup Zoo Cougar or a Kelly Galloup Heiffer Groomer in black. All three of these patterns have the collared head which push water as they are retrieved. The collar sends out an acoustic signal that allows the predator fish to locate the area where the fly is. The black color then provides the strongest silllouette at night so the predator can see the fly.

I would cast down and across and bring the fly back across the holding position of the fish. Use the appropriate weight or a sinking line to get the fly down.