Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_17839_1 ( length VARCHAR, map_colour VARCHAR )

### Question ###
When turquoise is the map colour what is the length?

### Accurate SQL ###

SELECT length FROM table_17839_1 WHERE map_colour = "Turquoise"