dal 9tanks, to answer your question the river auth.have put up an electronic barrier to count the number of different types of fish that go into the main river. Durham has a few weirs and the last weir tumbles into the main river Wear. The fish counter which is really a clever piece of machinery counts what tumbles over. I think a certain amount are "allowed" to go over, but if it is excessive they put a huge net across the river for a few weeks. We have a lot of fishermen here in these parts.