Tides flood into the salt marsh twice a day and bring salty water from the sea. Then twice each day the tide ebbs and leaves the salt marsh high and dry. The tides are at their highest (and lowest) near the new moon and the full moon, when the combination of the sun and the moon pull the tides up higher. These high tides, which occur twice each month, are called spring tides because the water seems to spring up. When the moon is half full, the pull of the moon and sun cancel each other out, and the tides are not as high and low. These tides are called neap tides and also occur twice a month.