Just be aware that some boat owners may get grumpy when you fish their docks. I'm quite sure they can't actually do anything about it though.
I am not a lawyer, and this is not legal advice, but I was curious, so I looked into this and it depends on where you are... exactly. In general, the harbor is "Tidelands" and therefore Public Trust Land owned by the citizens of California, however, the issue is where the "Tidelands" begin and where "private property" ends. There is a "bulkhead line" and a "pierhead line" and public water starts and ends at the bulkhead line. On the peninsula, the bulkhead line is defined about halfway between the end of the longest docks and the shore. For Balboa island, the bulkhead line is basically the boardwalk and everything on the harbor side of that is public water (in other words, "public" water extends all the way to the beach). Regardless of public water, the docks themselves are still private and touching them is trespassing.
Homeowners pay for the construction and maintenance of the docks and they also pay rent to the City of Newport for the privilege of having their dock on a public waterway. Someone shelling out $800/yr for dock space rental is likely to feel that whatever water is around that dock is also theirs, which may or may not be true, depending on where you are.
There are also a few exceptions, like the Linda Isle lagoon which are not considered a Tidelands public waterway.
You can check it out here (pdf)
Residential Piers