This Templar Hunt location can be found on the southern bank of the Thames river between the City of London and Southwark boroughs. As far as Templar Hunts go, this one is fairly easy as there is no optional objective to kill the target in a specific fashion and thus you can approach it in any way that you want.

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The target can be found on a barge (left). Once you have killed him throw his body in the river for the optional objective (right).

The target is located on one of the barges towards the western end of the restricted area. I found it useful to climb to the top of one of the ship masts here to get a nice view over the area and tag the enemies and target with Eagle Vision.

Once you have killed the target, to fulfil the optional objective for this Templar Hunt you need to throw his body into the river. After doing so escape the restricted area and become anonymous to complete the activity.