Water as a resource is now widely studied by scientists and economists. There are two current problems: supplying all human beings with water resources, which are diminishing per capita, and monitoring the potentially catastrophic water power during floods. The search for practical solutions to these problems is urgent. Each solution, however, must pass through a legal system which will ensure efficacy. The thirteen centuries of Roman history (with the reflections of the Mediterranean culture) have created, despite the diversity of places and knowledge, a unitary system, where the Roman law was the most important unifying factor. The aim of this paper is to examine the most important legal means to protect the environment, in particular the banks of the rivers, stressing the role played by the procedure called interdicta. The different legal solutions and their motivations proposed by the lawyers, remain of high interest even today, especially in view of the current debate between public and private interests. The role of interdicta and case law relating to them are the elements of a legal history of environmental protection. The Twelve Tables (450 BC) already foresaw the possibility of damage from rainwater. The classical jurists worked out a specific action (actio aquae pluviae arcendae) available against the owner of the land where it happened (even from an indirect human intervention), some work that altered the natural flow of water. The same action, in the era of Justinian, is used in the East to protect the right to receive water (precious and much scarcer than in Rome). An ancient instrument normally used for relations between individuals was the interdicta or orders of the magistrate to enforce certain behaviour. In case of disobedience, it prompted a private trial, which was very important in the protection of the coasts. Reported here are some fragments of the Digest of Justinian, where we read that in the event of an alteration to the navigability of a river or the safeguard of the ripae, the praetor will issue a special interdictum prohibiting to change the natural flow of a river, its airworthiness, and the integrity of its banks. The consideration of the applicability of legal prohibitions marked the emergence of a concept of public interest in the protection of the ripae for their usus publicus above the right of the riparian owner. In the Augustan age, Labeo offers an extensive application of the interdicta. We here emphasize that it is at popular legitimacy, that anyone can request it also through other pretorian instruments and that it achieves a fair balance between public and private interests. The interdicta realizes a simple, fast and flexible procedure. The interdictal procedure for the protection of public interests has enjoyed attention only by the latest Romanist because in the past the Pandectists looked at the Digest to create a system of individual rights and obligations. The adoption of a historical perspective promises to offer new insights on the actual interest on water resources.