In a situation where it's winter and two options are available, is it better to toivel in a river or in a lake? Which option is more preferable? Both the river and lake are "medium big".
When I asked the shaila to a renowned posek in the UK about my visit to East Europe where there is no mikva and toiveling stuff there, I was shortly told that "it's ok to toivel in a river in the summer", but when I asked "but it's winter now", I was answered something like "then rather use the lake".
Recently one of my friends, (who btw works in kashrus as mashgiach) told me that a river would be preferable even in winter. So i am asking.