New to river cruising. My husband surprised me by putting a Viking River cruise "on hold" for April 16-30 for our anniversary until midnight tonight (one cabin left). He didn't do any research on river levels (didn't even know this could be an issue). A friend told him about it and he was sold but the friend didn't go in the spring. I tried reading reviews but wanted to ask the experts here. What are the chances of the river being too high in mid to late April for this route? I would be disappointed if we were on a bus or switching ships many times. It is on Viking Gefjon, Grand European Tour. He wants to book ASAP. Thanks.