On this map, the green rectangle at upper right is JR Bibai station. You can tell it's 11km straight stretch toward the left, then another 2.3km after the turn (the marshland is marked by a blue line with a duck in it, inside a pink rectangle). I would not call this a walking distance.
http://www.city.bibai.hokkaido.jp/miyajimanuma//18_akusesu/18_akusesu....They do seem to have some community buses running, but the timetable is quite limited:
http://www.city.bibai.hokkaido.jp/miyajimanuma//18_akusesu/18_bustimet...The two tables on the left of this PDF shows the Bibai - marshland schedule, but still you need to walk at least one kilometer from the bus stop to the marshland.
The left top table shows the schedule on days when there is school, Mon. through Friday.
Departure from Bibai station: 14:33, arriving Bunkiten bus stop at 15:10.
THe next one from Chuo Elementary school 15:40 (arriving Bunkiten at 16:10) needs to be booked with a local driving school.
To Bibai station:
7:31 departure from Bunkiten
16:50 departure from Bunkiten (this one needs to be booked with a local driving school.)
The left bottom table shows the schedule during school breaks (no service on Sat., Sun. and national holidays)
The top four buses are from Bibai station to Miyajima-numa iriguchi (Miyajima marshland entrance)
The bottom four are from Miyajima-numa iriguchi to Bibai station.
Once again, the last one needs to be booked with the local driving school.
Even as a Japanese, I find the tables confusing.
