I know streamers with over 10 000 subscribers, which alone is $50,000 a month (Twitch takes a big cut of that but still). On top of that they receive donations every few seconds, in the range of $2 to hundreds. It's not unusual to see donations over $1000. Most streamers are completely transparent about their donations since they show up as notifications on the stream and the streamer thanking them.

Also, most streamers make pretty good money from referral programs.