I give up!
)*)&
This is the account but no definite location is given:
After successfully capturing Anglesey, Luke de Tany's men constructed a bridge of boats across the Menai Strait which separates Anglesey from the mainland. Edward's plan was to cross the River Conwy while de Tany crossed the Menai and attacked from the north. However, de Tany ignored the plan, believing he could defeat the Welsh without Edward's aid. He had contacted some of the clergy in Bangor who had promised to aid him by giving a signal when the time was right to attack.
The bridge was finished in September that year, and on 6 November, de Tany and his men crossed the bridge having been given the signal to attack. Llywelyn ap Gruffydd had been alerted to the crossing somehow, and emerged with a large army to meet the English as they crossed. A rising tide cut off de Tany's men from the bridge. When they tried to flee, many of them drowned when their heavy armour dragged them under the sea. Walter of Guisborough wrote an account of the battle:
Which takes me back to my answer of Menai Straits West of the bridge.
