Curly water thyme

L. major, also known as Elodea crispa makes a dense submerged aquatic perennial that is excellent as an oxygenator, which has stems capable of hiding baby fish from predators. It enjoys ponds and slow moving water, where its mass of branches have numerous, linear, spirally arranged leaves. Plants occasionally produce very small pink flowers in summer, although these are often overlooked. Stems can reach 1m (3ft) long. Excess growth should be regularly thinned during summer to prevent it swamping the pond. Plants should be positioned in the pond at a depth of 25cm (10in) to 75cm (30in). As a general rule, plant one bunch for every square metre of your pond to ensure good water oxygenation. As this species can be invasive in the wild it should not be allowed to spread into areas outside your own garden.

Looks good with:

Cyperus involucratus
Nymphaea 'Marliacea Carnea'