Ferry from Sai to Hotokegaura

- Is the ferry from Sai the only way to see Hotokegaura?

- How do I get from Matsu to Sai? By bus can?

- Is the ferry terminal easy to find from Sai bus terminal?

1. In addition to the ferry from the Sai, it is operated from Wakinosawa. The departure time of it is 10:45 and 15:05.
http://www.shimokita-kanko.com/?p=10687 (Japanese)
It seems to have been operating from Ushitaki, but it is lack of information.
http://saikanko.sakura.ne.jp/access/access.html

2. It takes 2 hours and 10 minutes by bus to Sai from Mutsu terminal.

3. In order to take a riverboat tour in Sai, there is a need to stop by the information office of Arusasu, located in front of the bus stop. Acceptance of the boarding is done on the first floor of there. To the pier is a few minutes from there.
http://www.saiteikikanko.jp/boatguide.html (Japanese)

I write the alternative of your plan to go to Sai from Mutsu.
Instead of from Mutsu, if you go to Wakinosawa from Aomori, Sii Line is useful. It is possible to switch to Hotokegaura bound pleasure boat at Wakinosawa by making use of it.
http://www.sii-line.co.jp/route.html (Japanese)
http://www.sii-line.co.jp/tour/01.html#course

How do I get to Wakinosawa from Matsu?

I found out about the bus to Wakinosawa from Mutsu, it was found that it is inconvenient in order to get on the Hotokegaura bound pleasure boat. It will not be operated only four times a day. If you go to Wakinosawa by bus, you will wait 2-3 hours there.

I think in order to go to Hotokegaura from Mutsu City, as you know, means that the switch to pleasure boat from the bus in Sai is good.

So, where can I get the timetable for the bus from Wakinosawa from Matsu?

I mean, where can I get the timetable for the bus to Wakinosawa from Matsu?

For Matsu that you said, I guess it's correct Mutsu. The bus Wakinosawa-bound, to the departure time of the following at Tanabe bus stop, located in Mutsu.
http://www.jrbustohoku.co.jp/route/detail/?PID=1&RID=4&BID=335
Weekdays
6:50,10:45,13:45,17:45

Holidays, Saturday
6:50,12:45,16:40

I hope that it answers your questions.