Cormorants on the pond: how to protect your fish from an underwater fisherman (nets, lines, shelters)

The heron waits at the edge; the cormorant, on the other hand, dives. This large black bird with bronze reflections pursues fish underwater, all the way to the bottom, leaving little chance for a fish without shelter. On a pond or large basin, a few cormorants settling in during the winter can take a large proportion of the fish within a few weeks, and the survivors often bear injuries. The good news: its precise needs, especially for taking off and landing, provide highly effective means of protection.

Know your adversary: how the cormorant hunts

The great cormorant is a formidable underwater fisherman. It spots its prey from the surface, dives and pursues it while swimming, propelled by its webbed feet, then resurfaces to swallow its catch. An adult consumes a significant amount of fish every day, on the order of several hundred grams. Unlike the heron, it does not need shallow banks: a deep pond does not discourage it.

It does, however, have two weaknesses. First, it is a heavy bird that needs a stretch of open water to land on and, above all, to take off from, running across the surface. Second, it hunts by sight: a fish that disappears into a narrow hiding place escapes it. Effective protection measures rely on these two points.

When and where the cormorant attacks

• Especially in winter: wintering populations, which are numerous in our regions, seek fishing sites when natural waters are poorer or frozen.
• On bodies of water large enough for it to land on and take off from, or near a watercourse or lake it already visits.
• In groups: a cormorant that finds a profitable site may be joined by others.
• Early in the morning, often at a regular time.

Typical signs: fish missing in all sizes, including fairly large ones, survivors with scratches or beak marks on their sides, stressed fish that remain grouped at the bottom, and sometimes the bird itself drying its spread wings on a post or dead tree.

Protections that work

The net for garden ponds

A fine-mesh net stretched above the water over hoops or a ridge and secured to the ground approximately every 50 cm completely prevents access. It also protects against herons and cats. The net must never touch the water and should be checked regularly to prevent a bird from becoming entangled.

The wire network for ponds

On a pond too large to cover, thin wires or cables are stretched above the water, either parallel or in a grid, between posts planted along the banks. Cormorants can no longer land on or take off from the water safely and abandon the site. The spacing between the wires is the key: if it is too wide, the bird slips through; the tighter it is, the more reliable the protection. Make the wires visible with ribbons or markers so birds can see them and avoid injuring themselves.

Submerged refuges

Large-diameter pipes, slatted crates, bundles of branches or purpose-built structures placed on the bottom provide fish with hiding places where cormorants cannot follow them. They greatly reduce losses without eliminating them, and also help against herons.

Bird scaring

A bird-of-prey-shaped kite attached to a long pole can deter cormorants on a large, open site. Like all bird scarers, it loses its effect if left in the same place: move it regularly and combine it with a physical barrier.

A protected bird

Like all wild bird species in the European Union, the great cormorant is protected by the Birds Directive. Exemptions exist, but they are regulated by the authorities and concern particular situations such as fish farms. For a pond or lake owner, the solution is physical protection and scaring, never destruction.

After an attack

The survivors are stressed and sometimes injured. Monitor the wounds, maintain very good, well-oxygenated water quality, and reduce feeding while the fish remain hidden. A wound that turns white, becomes covered in fuzz or gets larger warrants veterinary advice.

Read also

The other great fishing bird: Why fake herons repel herons

READ THE ARTICLE

Frequently asked questions

— Does a deep pond protect against cormorants?

No. The cormorant dives and pursues fish to the bottom. Only narrow shelters and barriers above the water are effective.

— Do cormorants visit small garden ponds?

Less often, because they need enough surface area to land and take off. Large ponds and lakes are the most exposed.

— What is the best protection for a large lake?

A network of wires stretched above the water, supplemented by submerged shelters and scaring devices moved regularly.

— Can cormorants be shot or trapped?

No. It is a protected species; exemptions are exceptional and regulated by the authorities.

In summary

• The cormorant hunts underwater, by sight, often in winter and in groups.
• It needs a clear stretch of water to land and take off.
• Netting for ponds, wire grid for lakes.
• Submerged shelters save some of the fish.
• Protected species: deter them, don't destroy them.

Last updated: September 28, 2026.