In the US navigable waterways (rivers etc) are controlled by the federal government. It’s in the commerce clause. There’s also probably a reason for this related to the federal government’s role in resolving disputes between states and rivers flowing among and through multiple states.
Since it controls rivers, the government is also responsible for guarding against flooding, etc. from this stems the Hoover Dam, the Tennessee Valley Authority (damming and electrification of the south), etc
Although this is seemingly only my own belief, I get the sense that the difference between how those things are handled even between the USA and in general how that relationship exists in Europe, is the strong emphasis of separation of powers that was constituted in the US's fundamental governing premise.
In Europe, generally speaking the government is largely dominated by the legislative today (whereas it was dominated by the aristocracy prior to WWI, generally). In the USA, the Constitution explicitly separates the Legislative of making the rules/laws; and the Executive, the enactment of the rules/laws ... the rule making and the acting body of the government. That is a notable difference from Europe where the lines are not drawn as clearly and the military, the body generally charged with security the health of the society, is subsumed and subjugated to the legislative, not at all on equal corollary to the government bureaucracy the way that it stands in the USA, where the military is not a body under the legislative the way it generally is in Europe, but rather an equal part to the Executive, acting body.
It's quite a nice balance actually in terms of preventing military control, while also not suppressing the self-preservation requirements of a healthy society the way that has been done in Europe, largely intentionally. It's a larger topic in and of itself, but the artificial suppression of both military and social self-preservation in Europe was very much the reason that the USA (mostly) has been serving as a kind of paternalistic helicopter parent over Europe, because the transatlantic aristocracy has intentionally and artificially suppressed Europe's health, immune system, and therefore basic human self-preservation instincts.
It's a great tragedy actually, and may one day be recognized as the great atrocity it is, a kind of national Munchausen Syndrome by Proxy, which will only result in Europe suffering the invariable grave consequences from such actions, be it total vanquishment, conquest, and occupation of their societies by foreigners in a kind of civilizational implosion we only know from the history books, or some other erratic outcome from a backlash against actions that have very much predictable equal and opposite reactions.
They are not all soldiers, the corps has considerable civilian staff as well. But the reason is mostly historical. The corps existed first to build and maintain coastal fortifications and then when the western frontier opened up it made sense to assign them to secure the rivers and improve the waterways west (the western expansion was as much a military operation against the native peoples as it was a civilian migration).
https://en.m.wikipedia.org/wiki/Navigable_servitude
In the US navigable waterways (rivers etc) are controlled by the federal government. It’s in the commerce clause. There’s also probably a reason for this related to the federal government’s role in resolving disputes between states and rivers flowing among and through multiple states.
Since it controls rivers, the government is also responsible for guarding against flooding, etc. from this stems the Hoover Dam, the Tennessee Valley Authority (damming and electrification of the south), etc