Just recently, I went back to Zion to hike the Narrows. The Narrows is the narrowest part of Zion Canyon. It is beautiful gorge with walls a thousand feet tall.  We started at the Temple of Sinawava on a paved road called the River Walk and hike in about a mile before entering the Virgin River. 
 
The hike is absolutely breathtaking as you walk upstream through the Narrows.
The water levels fluctuate depending on what time of year it is. I would say at this time of year the hike is moderately difficult if you are planning an all day hike up to Big Springs. Most of the way up you are about knee deep with frequent pools up to high waist deep. Some parts are slippery so poles are highly recommended. You can rent all gear (boots, pants and poles) in Springdale just outside the park at the Outfitters. 
 
This hike is definitely a favorite in Zion National Park. Even if you are just wanting to go and wade up stream for a half day or a few hours, it’s definitely rewarding and so much fun. 
 
Start as early as you can and bring layers even if its supposed to be warm as there is very little sun on this hike.  I would say the best time to do this hike would be late spring into early summer.