were there any water routes?
Yes, from St. Michael, at the Yukon River delta, a river boat could then take the prospectors the rest of the way up the river to Dawson
Klondike Gold Rush
From St. Michael, at the Yukon River delta, a river boat could then take the prospectors the rest of the way up the river to Dawson, often guided by one of the Native Koyukon people who lived near St. Michael. Although this all-water route, also called "the rich man's route", was expensive and long – in total – it had the attraction of speed and avoiding overland travel. 
when did the gold rush start in alaska August 16, 1896
wiki:13575390
Klondike Gold Rush [SEP] All water routes
It was possible to sail all the way to the Klondike, first from Seattle across the northern Pacific to the Alaskan coast. From St. Michael, at the Yukon River delta, a river boat could then take the prospectors the rest of the way up the river to Dawson, often guided by one of the Native Koyukon people who lived near St. Michael. Although this all-water route, also called "the rich man's route", was expensive and long – in total – it had the attraction of speed and avoiding overland travel. At the beginning of the stampede a ticket could be bought for $150 ($4,050) while during the winter 1897–98 the fare settled at $1,000 ($27,000).