Oroville is an overall safe town. Because most people drive, there are few if any petty crimes such as pickpocketing or mugging. There is an underbelly of methamphetamine producers and users in the town, which tend to be focused in the area known at "South Side", roughly bounded by Lincoln, Wyandotte, and Ithaca. Although this is an over-simplified definition, there is little reason for a visitor to go to this area, so it should be a non-issue.
The area just East of HWY 70 and between Oro Dam Blvd and Ophir road has been heavily contaminated by the chemical waste leftover from wood processing back when Oroville was a more prominent lumber town. Needless to say, it's advisable to not spend any time in this area, although again, it offers next to nothing as far as attractions unless a trip is needed to the local garbage dump for some reason.
While the area is low in humidity, the summers get incredibly hot, usually staying at a minimum of 37C/95F from June through August and sometimes peaking to 48C/120F. This makes for great fun at the lake or on the river, but when not on the water, make sure to stay very hydrated and wear sunscreen.
On the other end of the seasons, the winters are quite cold. While snow is extremely rare, it will often get below freezing which creates the hazard of "black ice" when driving. Also to note is the period in late January or February when a longterm fog settles in for a week or two that is quite cold, but more importantly makes for very hazardous driving due to decreased visibility. Make sure to take care and reduce speed as during this time there are often large pileups on the freeways of multiple cars.
