A family of beavers took up residence in Alhambra Creek in Martinez in 2007 and quickly did what busy beavers have always done — they built a dam. A fine dam it was, too, growing to thirty-feet-wide and six-feet-high at its height in winter 2007, before heavy rains crumbled it. The city has been flummoxed ever since about what to do about the beavers. The critters’ obsessive building, which recommenced right after the dam’s partial collapse, threatens an elaborate $10 million flood-control project undertaken after a series of early-21st -century winter storms routinely flooded downtown businesses and homes. The city council considered having the beavers exterminated or moved, but public outcry squashed those proposals. The beavers’ biggest allies are the hundreds, if not thousands, of people from near and far who are enchanted by watching their dam grow and by seeing them swim, diving into the creek, and gliding below the surface, with a graceful side-to-side motion of their flat tails. This spring, a couple of baby beavers were born, making up, perhaps, for a beaver that got sick and died in 2007. It’s easy to spot where the beavers may be — look for the people peering over the rail or sneaking down to the creek bed beyond the “no trespassing” sign.