Your dog smells the water and heads for the bank, dragging you behind. A river edge can hide a steep drop, strong current, or unstable ground. Do not use the edge as a test of your dog's recall or loose-lead skills. Keep them on a secure, well-fitting harness and a lead short enough to prevent them reaching the hazard. If you cannot safely hold them there, choose a route farther from the water.
Check local conditions and signs before walking near any body of water. Avoid fast or polluted water, ice, and places where you could be pulled in. A long line can create a dangerous run-up and tangle near the bank, save it for a safe open area away from water and other users.
Make the safer route worth taking
Practice loose-lead walking on an easier path, rewarding your dog for moving near you and offering sniff breaks away from the edge. Teach a cheerful turn cue at home and in a quiet outdoor spot before needing it by the river. As you approach a distant view of the water, reward your dog for noticing it and returning with you. Leave while they can still respond, if they lunge, you were too close for learning.
If swimming is appropriate for your dog, plan it separately in a suitable, supervised place after checking water safety. Pulling you into a river is not the price of giving them a fun outing. Ask a qualified, reward-based trainer for in-person help if their strength makes walks unsafe. After choosing a route where the river is out of reach, the loose-leash walking guide can help you practice slack-lead walking elsewhere. Do not make the water's edge a training test.
Sources: Dogs Trust: Keeping your dog safe around water. Dogs Trust: Dog walking problems and pulling on lead.