The migration of European eels is one of the miracles of nature. They start life in the great deeps of the Sargasso sea in the north-west of the Atlantic ocean as tiny, flat creatures, like almost transparent willow leaves, which drift 3,700 miles on the Gulf Stream to Britain and mainland Europe. The journey can take more than three years. When they approach Europe they make their first metamorphosis into ‘glass eels’: thin rods, shorter than a finger, which are also virtually transparent. These in turn have their own metamorphosis into elvers, which are essentially tiny eels. They swim upstream, close to the bank to avoid the river’s current, and slowly change into ‘yellow eels’. At this point they distribute themselves into streams and ponds, lakes and meres — anywhere where there is water.