Head Island Causeway tidal flow, Boston

Head Island is no longer an island, but merely a little bump in about a mile of causeway cutting off a small bay from the ocean---except for two small bridges through which water is still allowed to flow. This means that as the tide changes, a boiling current runs in or out beneath the bridges, equalizing the water back and forth. Here we see the tide is coming in, and hence water is rapidly streaming from the harbor into the little cut-off bay.