Severflot in summer and autumn operates passenger boats on the Yenisey and Ob rivers, from Omsk in the south to Antipayuta in the north. On this river-forum post, someones writes that Обязательно привезти копию первой страницы паспорта и копию свидетельства о рождении (emphasis mine) (Google translation: "Be sure to bring a copy of the first page of the passport and a copy of the birth certificate"). I would have a па́спорт (passport) in any case, but the need for a свидетельство о рождении (birth certificate) makes me wonder if they might limit foreign nationals. There are certainly places with travel restrictions for foreign or even Russian nationals. On the other hand, the eastern Siberian Lenaturflot advertises in English that Also voyage Yakutsk – Tiksi is popular among tourists from Russia and foreign countries. Usually such tourists come to Yakutia without taking a package tour. As a foreigner, can I simply buy a ticket on one of those river boats or might some be for Russian nationals only?
It seems to me that Salekhard is neither in border proximity zone nor in the list of territories where international citizens' travel is controlled.
Neither is Ob' river waterway.
However, Antipayuta seem to be deeply inside the territory where travel is controlled, which means, you will need a permit obtained from FSB to set foot there. It is also in border proximity zone with similar limitations.
Please see the following map: everything to the right of line requires explicit permit.
Of course, you also need to ask Severflot if they will carry international citizens, either way.