Perhaps one of the most noticeable unintended consequences to the construction of offshore breakwater structures is the increase in the amount of urban runoff and various forms of water pollution that develop between the breakwater and shore. In an unmodified environment, the natural wave action would keep such pollution diluted and dispersed, but the calmer seascape these barriers create also prevents the sea from performing its cleaning duty. The result is often dirtier beaches.
More intense wave action brings surfers and other sorts of water recreation activities, along with their accompanying tourist dollars. Tame waves that breakwaters create can have an adverse economic impact on an area. The city of Long Beach, California, is experiencing this type of situation firsthand, according to the Surfrider Foundation, an organization seeking to do away with the barriers in order to return the coastline to big waves and the associated financial boom they hope will occur.
The primary reason breakwaters are built in the first place is to protect shipping ports from the full strength of open ocean waves. This protection makes for easier, safer and more productive shipping patterns -- which companies that use the port demand -- thus is created an impasse between two points of view, neither of which is all right or wrong. On one side is safer shipping ports and less rearrangement of sand on neighboring beaches; on the other is a return to natural conditions.
Even though one of the stated goals of a breakwater project is often to keep beaches from eroding away, artificial structures rarely cause exactly the intended result. While it might stop area beaches from losing sand to downshore drift, the sand has to go somewhere. Normally it simply piles up at the foot of the breakwater, where it touches the shore, sometimes creating shallow, stagnant water and sometimes exciting and often dangerous conditions, like the famous Wedge, in Newport Beach.