Making a bigger channel may change the patterns of water circulation in the lagoon. Building a causeway between islets may cut off flows of water important to maintaining the quality of the lagoon, and can even block the migration routes by which fish go in or out to feed. All these changes will have their effects on lagoon life and productivity. Wastes and other runoff from the land may also collect in a lagoon and pollute it. Some islands have had cholera epidemics spread by the pollution of seafood caught in the lagoon.
Lagoons are particularly vulnerable to the development of towns or cities around their edge.
Since a lagoon is usually a single system, the whole lagoon is usually affected by damaging activity. It is not usually possible to reserve or protect just one part of it. Lagoon management Lagoons generally have to be managed as a whole for multiple uses. Each activity has to be developed carefully to be sure it fits with all the other uses. The way the lagoon system works must be studied in detail before deciding to make major changes.