pictures of the layout of the pond and what the trees look like in the pond would help us. If they are in shallow water drawing the pond down may help cut them. If they are going to be in the way of your prime fishing spots (if you cut them down at ice level and the vertical portion under ice is still in the way) then... you may want to draw water down and use a dozer to push them over. You need them 6' tall or so so the dozer can use the tree itself to push the root ball over. You could then decide to cut the usable lumber and leave the root ball partly in the ground yet to rot or to serve as fish cover and use the logs for lumber or fire wood?

If they are in deep water then cutting out of a rowboat is not so fun. Then you are probably best off using the ice as a more solid platform to cut trees down and remove the wood and branches.