Problems with Mann-Kendall trend test

Dear R users,

Can anyone help me with mann-kendall trend test? I tried to use the newest
packages 'trend', and the function mk.test, but had problems in applying
the input data.

For example, res <- mk.test(Nile), Nile is a time-series data. But when I
use my dataset, with one column which is a time-series data, it says
"error: input must be ts object". How to do this? Thanks for your help.