I'm trying to run bwa index, but I keep getting this error:

[bwa_idx_build] fail to open file 'bwtsw' : No such file or directory. 

My code is:

for ref in *.fa; do\
bwa index $ref -p $ref -a bwtsw\
done

The files in *.fa are: Mix1_S1_CNS.fa Mix2_S2_CNS.fa Mix3_S3_CNS.fa. They are consensus sequence fasta files generated by using samtools consensus on previously aligned bam files. I suspect these files I'm trying to use as references are causing the issue, but I don't understand why the error is related to the algorithm tag.