Safe for woman to travel alone in Dar/Zanzibar? (Dar es Salaam)

Hi all

Hope you can help me with some tips / info on travelling in Dar/Zanzibar area.

I'm going to be travelling most likely alone (blond woman), and been hearing mixed reviews if it is safe or not... Hopeing to do some diving in Zanzibar area, so if you have trustworthy tour operators/hotels/etc that could perhaps arrange also transport from Dar to there, would be great!! All tips/info in general highly appreciated.

BR,
Marjo