The Maly Dunaj River is a calm river and its current is not very fast, generally. But some parts of the river are a little faster and if your canoe hits a hidden limb or tree, your canoe can capsize easily. Just below Vlky you should be aware of such hidden dangers and try to sail in a middle of the river to be safe.
You may need from 3 up to 5 hours (with rests) to sail down from Vlky to Jelka - Ister Restaurant. Then you can paddle till Jelka Water Mill another 1.5 hour.