Eve,
Yes that's a piglet swimming - pigs are natural swimmers, and the largest pig swims quite happily and strongly.
In Japan they breed Berkshires, and swim these every day to improve muscle tone. They also then oil them. The resultant meat is a real speciality and much in demand.
This photo was a pond in a field that we don't keep pigs on. We were walking a sow and her litter through this field, and she decided to nose round the pond. It was a warm day, and a couple of piglets started paddling and then they just pushed off and swam round. They are really strong and confident swimmers. We ran back to the house and grabbed the camera!
Both ponds and rivers/steams do not generally make good places for pigs.
Pigs have escaped from properties where the owners have thought a stream or river would make a good boundary, and the pigs have just swam across or down the river to next door !
Rivers/streams also have two further problems. Firstly you have no idea what pollution is coming downstream that might harm your pigs, and secondly you will be introducing both dung and urine into the river/stream, polluting this for downstream.
On ponds, you need to consider from two angles. Firstly risk to your pigs, and secondly impact of your pigs on the pond.
Ponds will be of three types (may be more, am not a geographer!). Stream fed ponds have the same problems as above on pollution. Spring and dew ponds can quickly become mud and stagnant if pigs are introduced, making them into a wallow at best. In both cases you may upset local wildlife that depends on these ponds, both insect, fish, birds, and even deer that use these as their water source.
Finally the bottoms of natural ponds can be full of leaf debris, that once stirred up can make a real mess and ruin the pond, but also give a "quicksand" type bottom that can potentially trap your pigs - large sow more of risk that 8 week weaner, but not sure how you’d get either out without the fire brigade!
Now before I sound too precious, that old dip in the ground that is just a muddy mess is somewhat different from the glistening clear ponds that Bambi drinks from, and I would not say never incorporate a pond, but in general we recommend that you exclude them.
Finally, you can buy yellow armbands for your pigs!! Not Joking - Yes you can - they are used to support the heads of just born weak pigs whilst immersing them in warm water (which both warms the piglet and helps blood circulation).