When a seaplane is on the water, FAA, Coast Guard, and local water rules all apply.
91.115 Right-of-way rules: Water operations.
(a) General. Each person operating an aircraft on the water shall, insofar as possible, keep clear of all vessels and avoid impeding their navigation, and shall give way to any vessel or other aircraft that is given the right-of-way by any rule of this section.
(b) Crossing. When aircraft, or an aircraft and a vessel, are on crossing courses, the aircraft or vessel to the other’s right has the right-of-way.
(c) Approaching head-on. When aircraft, or an aircraft and a vessel, are approaching head-on, or nearly so, each shall alter its course to the right to keep well clear.
(d) Overtaking. Each aircraft or vessel that is being overtaken has the right-of-way, and the one overtaking shall alter course to keep well clear.
(e) Special circumstances. When aircraft, or an aircraft and a vessel, approach so as to involve risk of collision, each aircraft or vessel shall proceed with careful regard to existing circumstances, including the limitations of the respective craft.
AIM 7-5-8 also discusses seaplane safety and best practices. One item covered there is that seaplanes on the water have the right of way to depart over seaplanes in the air, as the airborne seaplane has better visibility and most likely would prefer the other aircraft out of their way anyways.
Seaplanes are exempt from USCG safety equipment requirements, however, FAA and State requirements do apply.
Where can you land?
Seaplanes have as much rights as power boats to use waterways and sometimes more. You must ensure that Federal, State, and local regulations do not prohibit seaplane operations. Generally, if powerboats are on the lake, you are likely, but not guaranteed to be able to be there as well in your seaplane. To be sure, check the Seaplane Pilot’s Association Water Landing Directory App on your smartphone.
Buoys
There are lots of buoys that mean lots of different things. The easy ones say on them what they mean. For the ones that do not have marking or words on them, common sense will have to apply.
Call or ask locals in the area what the non-standard buoys mean when you are unsure, and as a general rule, don’t get to close, it may be marking a hazard.
As for red and green channel markers, we use the three “R”s. Red, right returning. That means when you are returning from open water or proceeding upstream, the red channel markers will be on your right-hand side. While I find this has little importance in operating seaplanes, it is a small fact that may help you one day, an is often asked on oral exams.