The flow rates on the Little Juniata river at Spruce creek can be accessed by clicking the link below. Here are some subjective opinions for different flows:
90 to 150 CFS = Low Flow. Wade anywhere. Check water temps, consider fishing elsewhere. No floating possible unless you want to drag a lot.
150 to 250 CFS = Low to Moderate Flow. Wade with a little caution. Kayaks and canoes with some dragging.
250 to 350 CFS = Moderate and very fishable flows. Wade with caution and take a staff. Floating with only a couple of short drags.
350 to 550 CFS = Medium/high flows. Still fishable if clear enough. Wadeable in many places and use a staff. Easy floating of light crafts. No drift boats.
550 to 750 CFS = Fishable if clear from shore or boat. Wading in only a few locations. Not worth the risk. Some class 2.5 water. Any watercraft will do. Watch for strainers under limbs.
Over 750 CFS Forget it ! Dangerous. Throw Streamers from the rocks if you must do something.
A link to the realtime flow rate data at the USGS site upstream of Spruce Creek.