What happens to wildlife when a river floods?

For much of the year the River Mole is a quiet, sluggish, muddy, shallow waterway meandering through lush green fields or fields shady woods near Betchworth. But a few times a year it changes its form.

Rivers like the River Mole have always flooded. Long before roads, houses, and flood defenses, winter rain spread across the valley floor, eroding the land and creating the fertile soils of the Mole Valley.

When a river floods, it can look dramatic — even alarming — to us. Fields disappear, paths and even roads may vanish, and familiar landscapes seem suddenly out of control. And, it can be very damaging if it spills into properties.

In January 2026, after several days of heavy rain, the River Mole flooded onto the fields and woodlands near Betchworth and Brockham. It seemed like a disaster for the wildlife but many of the plants and animals that live here have evolved with this natural cycle — and some animals depend on it.

Fish are often the first to respond. As water spills out of the main channel, it creates temporary side pools and flooded meadows. These calm, shallow waters are rich in food and safer from predators. Fish move into them to feed, rest, and sometimes to spawn.

Amphibians — frogs, toads, and newts — thrive at this moment. Floodwater connects ponds, ditches, and streams that are usually separate. This gives amphibians new routes to move, breed, and spread their populations across the landscape. Invertebrates respond in their thousands.

Worms, insects, and larvae are lifted from soils and leaf litter and carried into new places. When the water recedes, they leave behind a rich food source — especially important for birds. Birdlife changes quickly during floods. Waders and water birds arrive to probe the soft mud for invertebrates. Ducks and swans feed on flooded grasses. Kingfishers and herons take advantage of fish in shrinking pools.

Mammals adjust too. Water voles retreat to higher ground but return quickly once levels drop. Foxes and deer follow the water’s edge, feeding where floodwaters uncover fresh vegetation. Even bats benefit, as floods trigger bursts of insect life once waters begin to fall. When a field floods, the most important changes happen out of sight, beneath the surface. As water fills the soil, it pushes out the air held in tiny spaces between soil particles.

Oxygen quickly disappears, and the soil becomes waterlogged. This sounds dramatic, but it is a condition soils have experienced for millennia. Soil life does not stop — it adapts. Microbes that need oxygen slow down, while others take over, quietly breaking down organic matter in different ways. Nutrients such as nitrogen, iron, and phosphorus are released and reshuffled, changing the soil’s chemistry for a time.

Most soil animals sense flooding early. Earthworms, insects, and larvae move upward, sideways, or into temporary shelter. They are not wiped out — they wait. When the water drains away, oxygen returns, microbes surge back into activity, and plants respond with fresh growth.

Flooded soils are not damaged soils. They are soils resetting — part of a living system that knows how to recover. As water spreads and slows, it drops fine sediments — natural fertiliser — across meadows and floodplains. This is why river valleys are often so rich in wildflowers, grasses, and insects. To us, floods can feel like nature misbehaving. But ecologically, they are moments of renewal. They reconnect habitats, redistribute life, and reset the system. .So when the river rises, it is a wonderful manifestation of the Earth interacting with itself shaping the landscape and rejuvenating life along the river corridor.