Take this from a former competitive swimmer (a not-slow one) now with 25+ years of lap swimming: This is far more complicated than the OP.
Reasons for a current:
(1) This is an outdoor pool. Sunlight is the death of chlorine in pools. The bigger the pool, the brighter the sun, the more chlorine is burnt off. The chlorine-related chemicals used in pools also do not properly dissolve in water. They slowly rise towards the surface. So when you turn off the circulation system, they rise towards that deadly sunlight. Given that, and the fact that they were having epic chlorine-related problems, it is of no surprise that they would have run the circulation systems as much as possible when the pool was not in use. But pool water doesn't stop instantly. A gyre may have formed and be stable for hours afterwards. Laneropes are meant to stop this, but they do little under the surface.
(2) This is an outdoor pool, in direct sunlight, with the pumps off during the day ---> convection currents. And the circulation system is off. This is most interesting because as the sun rises one would expect an asymmetric current to form based on which side of the pool got the most sun. Normally this would be, in the southern hemisphere, the south west corner. I would expect an upwelling there along the wall, with a much lesser current across the pool surface from SW to NE.
Effects of the current.
Head/tailwinds aren't normally an issue. The faster one swims the lesser the effect. If this were happening we would see it in differences between length splits (fyi "length"=50m and "lap"=100m, many confuse those terms). I think up/down-welling currents are more at play. Fast swimmers rely on very specific stroke patterns. Slight perturbations in the water can throw off a swimmer's stroke. Imagine swimming past a water jet or upwelling and your hand is pushed sideways. That can slow you down far more than fighting a slight current.
If I am correct, the greatest effect would be in the SW corner of the pool. Anyone know which lane that would be? In the footage, we should also see swimmers drifting (both left and right) when approaching that SW corner.
See those windows. This is an outdoor pool under a temporary structure. Sunlight (UV) is coming in and air is circulating. And if the the pumps are running, they aren't at full power during races. Often at such events officials will state that pumps are run when they are in fact off. This is a common conflict between the needs of the event (stable water) and local health codes that dictate that circulation pumps remain on. In a 50m pool, if they are on they aren't 'on' enough to keep things mixed.
Reasons for a current:
(1) This is an outdoor pool. Sunlight is the death of chlorine in pools. The bigger the pool, the brighter the sun, the more chlorine is burnt off. The chlorine-related chemicals used in pools also do not properly dissolve in water. They slowly rise towards the surface. So when you turn off the circulation system, they rise towards that deadly sunlight. Given that, and the fact that they were having epic chlorine-related problems, it is of no surprise that they would have run the circulation systems as much as possible when the pool was not in use. But pool water doesn't stop instantly. A gyre may have formed and be stable for hours afterwards. Laneropes are meant to stop this, but they do little under the surface.
(2) This is an outdoor pool, in direct sunlight, with the pumps off during the day ---> convection currents. And the circulation system is off. This is most interesting because as the sun rises one would expect an asymmetric current to form based on which side of the pool got the most sun. Normally this would be, in the southern hemisphere, the south west corner. I would expect an upwelling there along the wall, with a much lesser current across the pool surface from SW to NE.
Effects of the current.
Head/tailwinds aren't normally an issue. The faster one swims the lesser the effect. If this were happening we would see it in differences between length splits (fyi "length"=50m and "lap"=100m, many confuse those terms). I think up/down-welling currents are more at play. Fast swimmers rely on very specific stroke patterns. Slight perturbations in the water can throw off a swimmer's stroke. Imagine swimming past a water jet or upwelling and your hand is pushed sideways. That can slow you down far more than fighting a slight current.
If I am correct, the greatest effect would be in the SW corner of the pool. Anyone know which lane that would be? In the footage, we should also see swimmers drifting (both left and right) when approaching that SW corner.