Overall difficulty really depends on your skill level, but in general, outdoor rowing is a bit tougher for a couple reasons. First, it takes more practice. You have to get used to navigating the open water, and the feel of moving backwards if you’re using a true row boat. You also have to pay more attention to your balance and any potential obstacles you may encounter.   Water conditions can also be unpredictable. When you’re on an indoor rower, you don’t have to worry about waves or wakes from other vessels on the water. When you’re doing a rowing workout outside, you have to consider all of these factors and more.