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_name_97 ( tonnage INTEGER, nationality VARCHAR, name_of_ship VARCHAR )

### Question ###
What was the average tonnage for the Siljan ship from Sweden?

### Accurate SQL ###

SELECT AVG(tonnage) FROM table_name_97 WHERE nationality = "sweden" AND name_of_ship = "siljan"