Internal waters
The UNCLOS category landward of the baseline, the coastal state powers over it, and why an artificial canal falls inside it.
Internal waters are the waters on the landward side of the baseline from which the territorial sea is measured. The coastal state exercises full sovereignty over them, and there is no general right of innocent passage, so a foreign ship enters on the coastal state terms.
That category answers a question the law of the sea is often expected to answer another way. An artificial canal cut through a state land territory is internal waters, so the navigational rights in Part III of the United Nations Convention on the Law of the Sea never engage, and the rule in Article 26 barring a charge levied by reason only of passage has no application. This is why a canal toll is lawful and a toll on passage through a strait used for international navigation is not.
The full article will cover the baseline rules that define the category, the coastal state jurisdiction and its limits, the narrow exception preserved where a new baseline encloses waters previously not internal, ports and roadsteads, and the treatment of canals and other artificial waterways.