"""create lakes table

Revision ID: 1234567890ab
Revises: 
Create Date: 2023-05-25 10:00:00.000000

"""
from alembic import op
import sqlalchemy as sa
from sqlalchemy.dialects.postgresql import UUID


# revision identifiers, used by Alembic
revision = '1234567890ab'
down_revision = None
branch_labels = None
depends_on = None


def upgrade():
    op.create_table(
        'lakes',
        sa.Column('id', UUID(as_uuid=True), primary_key=True),
        sa.Column('name', sa.String, nullable=False, unique=True),
        sa.Column('description', sa.Text, nullable=True),
        sa.Column('location', sa.String, nullable=False),
        sa.Column('created_at', sa.DateTime, server_default=sa.func.now()),
        sa.Column('updated_at', sa.DateTime, server_default=sa.func.now(), onupdate=sa.func.now()),
        sa.PrimaryKeyConstraint('id'),
        sa.Index('ix_lakes_name', 'name')
    )


def downgrade():
    op.drop_index('ix_lakes_name', 'lakes')
    op.drop_table('lakes')
```

This Alembic migration script creates a new table called 'lakes' with the following columns:

- `id` (UUID primary key)
- `name` (String, not nullable, unique, indexed)
- `description` (Text, nullable)
- `location` (String, not nullable)
- `created_at` (DateTime, server default to current timestamp)
- `updated_at` (DateTime, server default to current timestamp, updated on each record change)

The `upgrade()` function creates the table and the index on the `name` column.

The `downgrade()` function drops the index and the table, effectively reversing the changes made by the `upgrade()` function.