A little island in the middle of your fish pond adds interest and is a place to grow a few extra ornamental plants. Generally, you include the island when digging the pond, but you can also add a simple floating island to small, established ponds. You simply need to ensure that the island is secure and won't collapse within a week. You also need to avoid using any toxic substances or stressing your fish during installation.
Select enough large, relatively flat pieces of lumber to cover the area the size of your planned island. Arrange them parallel to each other and bolt together to form a square.
Attach a few wooden slats to the top with nails, leaving narrow gaps between them for plant roots.
Attach the plastic drums to the underside of the raft with wire.
Hold everything together more securely by tacking wire netting into place over the entire island.
Attach a chain to the underneath of diagonally opposite corners.
Float the island and attach the other end of the chain to a large, heavy rock to secure the island in the middle of your pond. Otherwise it is liable to drift to one side. A bit of leeway on the chain lets your island move around a little; securing it very tightly keeps it anchored in one place.
Add gravel until the top of the island is a few inches above the surface of the pond. If you want decorations such as sculpture or rocks, put them on first, then add gravel to lower the island.
Add garden soil on top.
Add emergent plants to the island. Wetland plants suited to very watery habitats on the edges of ponds also grow well on pond islands.