Unfortunately we don't have a great track record of taking care of the commons. Communal ownership almost always leads to neglect of the owned thing - parks have paid employees to take care of them, so (sometimes, if there's enough money thrown at it) they stay clean.
Likewise, your criticism of private ownership is too extreme. The vast majority of landlords take excellent care of their properties for example. Others take the right amount of care so that the place isn't great, but can be rented for less. Some landlords let a place decay until it's unsafe, but that's usually when incentives are set up that its in their best interests to do so. Such incentives are the opposite of private property rights and are usually in the form of rent controls, etc, where you can raise rent only when you drive tenants out, or its not profitable to use a property as housing and the only way to change its use is through its destruction.
On the flip side, the example of privately owned waterways is a terrible one, because there's no way to avoid the communal, commons nature of the ecosystem. And companies might have a use for the lake or river (disposal of toxic waste) that is counter to the common interest, as you rightly point out. Then they poison everyone.
So: communal ownership. Suboptimal but we're stuck with it in many situations, so we need to implement it as effectively as we can.