During a walk on the mudflats, you are bound to find ulva growing in certain areas. The fishermen call it 'flap'. In Brittany, this green seaweed forms a plague. It is still a common species in the tidal regions around the North Sea however it has been declining in the past decennia in the Wadden Sea. This is because there are fewer nutrients in the water. Ulva readily tears off from its root, but continues to grow further just the same. Sometimes you see what looks like toilet paper on the flats or in the flood mark on the beach. In most cases, it is dried up ulva that has been bleached by the sun.