An algebraic expression is a mathematical phrase that contains numbers, variables (like x or y) and operators (like add,subtract,multiply, and divide).
We have to form the algebraic expression for the phrase
" The product of 86 and the depth of the river"
Let the depth of the river be 'd'
Therefore, the algebraic expression = Product of '86' and 'd'
=

= 86d.
Therefore, the algebraic expression for the given phrase is "86d".