As warm as it may be, I couldn't swim in the sea, since the temperature is not that high. But I could put my feet in the water.
ご質問ありがとうございます。
"As warm as it may be"＝「暖かいとはいえでも」
"I couldn't swim in the sea"＝「海水浴は出来ないが」
"since the temperature is not that high."＝「気温はそれほど高くないので。」
"But I could put my feet in the water."=「でも、海水に足を入れることはできる。」
ご参考に！
アメリカ合衆国 
