When shooting long exposures, in moving water or on some soft grass, our tripods can shake slightly. It maybe imperceptible, but it's clear when we look at our photos that this has happened.
Why is this? Mainly due to our tripods weighing so little these days. Carbon fibre tripods are strong as hell and super light (which is amazing for landscape and travel photography) but that weight loss means a gentle current in some water will be strong enough to vibrate our tripods, hopefully without knocking them over.
A low centre of gravity will help, so spreading the tripod legs wide so the camera is lower to the ground. If surface you are on is soft (like wet sand) then digging the feet and legs in will increase stabitlity. The best option I've found to eliminate most enviromental induced shake is to weigh the tripod down. I always have a plastic carrier bag or two in my camera bag and if needed, I'll fill one with stones or some other weighty substitute, and hang it below the centre of my tripod. You could use your camera bag instead but I don't like to. This will increase the downwards weight over the centre of the tripod and camera and hopefully stop camera shake.