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Can you boil you egg or food on Shabbat in this river?

פסחים מא, א

אָמַר רַב חִסְדָּא: הַמְבַשֵּׁל בְּחַמֵּי טְבֶרְיָא בְּשַׁבָּת — פָּטוּר. פֶּסַח שֶׁבִּשְּׁלוֹ בְּחַמֵּי טְבֶרְיָא — חַיָּיב

Rav Chisda said: One who cooks food in the hot springs of Tiberias on Shabbat is exempt. One violates the Shabbat prohibition of cooking only if he uses a fire. In the case of a Paschal lamb that was cooked, i.e., boiled, in the hot springs of Tiberius, one is liable for boiling the offering [for it may only be eaten roasted over a fire].

Rav Chisda’s ruling is based on the simple premise that the kind of cooking that is forbidden on Shabbat is that which involves fire. If you cook by another means, like for example, the sun’s heat, then there is no Sabbath violation. And according to the sages of the Talmud, the hot springs of Tiberius (and Yellowstone too, I presume) are heated by the sun. Hence there is no prohibition against cooking in hot springs on Shabbat. But before gently lowering your chicken into the waters, check with a park ranger first.