Not so sure how to tackle your problem because the edge of the pond can be restrained easily by ground anchors ( drill holes in soil, insert reinforcing bars and grout the hole up with cement grout), mini piles (same as ground anchor but always in vertical direction and in diameter around 100mm) or simply cast a concrete perimeter wall (with sufficient ballast weight) capping part of the pond.
To anchor the pond to the substrate you need to know the soil characteristic before sizing the anchoring system. With concrete perimeter wall, it is based on the amount of dead weight and is probably the easiest solution in your case.
The pond could suffer damage if the upward thrust at the middle is excessive while the edge is restrained ( I am assuming your pond has not been designed to withstand such bending effect). To restrain the inner part of the pond you may need to dewater it, knock holes through, form structural connections using any of the above and make good afterward.