This yellow flower is part of a plant and is an oval shape. It was found by the water. They form in bunches.
These were popular in this area. Also by the water.
On waste-ground. My thanks to Tom Belton (Department of Conservation, Hokitika) for ID.
Yellow rocket seedling (Barbarea vulgaris)
Early Winter Cress
Barbarea (winter cress or yellow rocket) is a genus of about 22 species of flowering plants in the family Brassicaceae, native to temperate regions of the Northern Hemisphere, with the highest species diversity in southern Europe and southwest Asia. They are small herbaceous biennial or perennial plants with dark green, deeply lobed leaves and yellow flowers with four petals.