The main trail at Jenkinson Lake follows the shoreline, it is an easy level 1-2 hike and most of the trail is shaded. The trials do cross through and follow some campground roads. When you are hiking on the roads please watch your step because the pavement can end sharply along the edges. The full hike around the lake is over eight (8) miles.
The Fleming meadow trail system is a great place for a hike. I also like to go down just past the lake on Mormon Immigrant Trail there is a parking area and a trail head you can hike around the lake with great views. If you hike in about 3 miles at the end of the lake you will come to a waterfall that is best seen in the spring. For an easy hike along the water come into the park and go to the group day use area and hike to the marina and back, it is a nice shady trail with great views.
For an easy hike to the Park Creek Waterfall enter the park at the main entrance and keep left at the fork in the road and proceed to the end of the park road, and park at Hazel Creek Meadow. There is a small footbridge across Hazel Creek and the waterfall is about a one mile hike. Below is a clip show of the hike and the waterfall.
Tom Steinstra has the best books on Camping and Hiking, I have found them very useful over the years.