Glad you asked...
Create your plan. Trench three feet deep and eight feet wide. Lace the insides with pool plastics leaving openings for your water guides. You will also need drainage.
Then again, this answer might help you...
To build a lazy river like the kind you might see in theme or water parks, you will need a great deal of room and water. The water will have to be kept moving with a large pump. If you have a waterfall, you will need another pump to move the water for that. You will need to line your river with rock or concrete.

