```ts
function tideMarks(levels: number[]): number[] {
    if (!levels || levels.length < 3) return [];

    const peaks: number[] = [];
    for (let i = 1; i < levels.length - 1; i++) {
        if (levels[i] > levels[i - 1] && levels[i] > levels[i + 1]) {
            peaks.push(i);
        }
    }

    return peaks;
}
```