Tvilas keilim in winter - better in river or lake? (if no mikva around)

Question

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 preferable? Both the river and lake are "medium large".

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.

Answer 1

We can't tell you about a specific river or lake without more details but can share the general laws of tvilat keilim in river and lakes. Note however that women should not immerse there without detailed instructions from their Rav ¹.

In summary

• a large lake, the sea or an ocean are kosher for tvilat keilim
  
• a smaller lake with spring water flowing in can be kosher if it hasn't rained recently and there is no concern of melted snow
  
• rivers sourced from springs can also be kosher but not if fed from melting snow - their rules are more complex and small details can be critical (e.g., the presence of a turbine upstream to produce electricity)

OU Kosher brings some general rules

The general rule is that spring water is acceptable for tevilah even when flowing, while rainwater and melted snow is acceptable only when stationary. In situations where there is a mixture of rainwater and spring water, we follow the majority: if mostly rainwater, the water must be stagnant, but if mostly spring water, the stream is acceptable for tevilah even when flowing.

Large lakes (which are viewed as stationary bodies of water), [seas] and oceans are kosher for tevilah at all times, even if it had recently rained.

Chabad adds

The water in most larger rivers is primarily sourced from springs, although the rivers may swell noticeably in the rain season. But my concern is more about mountain rivers, that flow only in the warmer weather, and are fed from the melting snow at the mountains' peaks. Melted snow has the same status as rainwater, that it is valid as a mikvah only when static, but not when flowing. So, you cannot immerse vessels in a mountain river.

See there as well as here for further details. And as always, check with your Rav for any practical ruling.

_{1. Practically, there are many issues which render immersing into a lake or river very delicate for women, and very often lead to non-kosher immersions. Examples are hatzitzot of earth while going down to the water, danger of currents, the fear of being seen which leads to being rushed and making mistakes, challenges of letting go of clothes, difficulties in checking the woman is ready for immersion or that it was done correctly, etc.}